Why are baroque harpsichord composition played most of the time on the piano?

You asked, "Also are there any changes which need to be made for a harpsichord work to played on the piano?" A change that technically could be made (but never is in my experience) is to retune the piano to one of the many non-equal temperaments that were used in Bach's time. The modern-day piano is tuned in equal temperament (http://en.m.wikipedia.org/wiki/Equal_temperament). The space between each adjacent note is the same. If you haven't thought about temperament before, the idea that adjacent notes may have different spacings might be challenging. Yet historically, equal temperament is a relatively new development. Theoretically, it was mentioned as early as Vincenzo Galilei (http://en.m.wikipedia.org/wiki/Vincenzo_Galilei) in the 1570s, but for very good and very practical reasons, it never gained a foothold until the demands of the music gradually pushed towards 12-tone chromaticism. Open, or non-tempered, intervals sound better. (There are no audible beats (http://en.m.wikipedia.org/wiki/Beat_(acoustics))) Pure 5ths are strong; major 3rds are sweet; and so on. When music doesn't change key or have extreme highs or lows, the sound of just tempered scales works better. Without getting into a discussion on pre-18th century modes and the historical development of chromaticism, let's just say that western classical music prior to the late 19th century suits a tuning system that is tempered towards the accuracy of a single or a couple of main key areas. The problem with just intonation is that intervals outside the home key can sound dreadful. During the eras when music didn't stray too far from home, this wasn't an issue. But music composition moved rapidly in the 19th century towards the total abandonment of the major-minor tonal system. The epitome of this can be seen in 12-tone technique (http://en.m.wikipedia.org/wiki/Twelve-tone_technique") music where there no individual note has dominance. This is so far removed from the "Doh a deer" level where tonic dominance is total! When the spacings are the same, we can change key or use 12-tone techniques with equal ease. But, you may ask, this sounds (pun intended) fabulous; why wasn't it taken up in the 1570s? Equal temperament leaves all intervals (aside from the octave) slightly out of tune. It's a compromise. And if you are used to playing 'pure' intervals, even the sound of the piano can be challengingly uncomfortable. Bach's music (to take the prime example) when played on a harpsichord resonates more fully in terms of the purity of the intervals than on a modern piano. Yet he wrote a series of pieces in every major and minor key each containing a high degree of modulation (key changes). How can this be done using just intonation on a harpsichord? This question is far too big for here. The answers vary and the Wikipedia article for The Well-Tempered Clavier ("http://en.m.wikipedia.org/wiki/The_Well-Tempered_Clavier") can provide some to the starting links to that discussion. What isn't mentioned there is the notion that Bach knew which intervals were "wolf", i.e. sounded dreadful, and used that knowledge to inform his choice of suspension, modulation and so on. It would be interesting to hear baroque music played on a well-tempered modern piano. Does anyone know of such an experiment?

You can use a piano for classical, jazz, rock, country, showtunes, and a million other things. You can only use a harpsichord to play, well, harpsichord music. In the NYU Steinhardt building where I go to grad school, pianos  outnumber harpsichords about a hundred to one, and I'm sure it's not an unusual music institution in that respect. Maybe if harpsichords were as common, people would feel more compelled to play them.

Notice that we could also ask "why are Beethoven's works played on modern grand pianos most of the time rather than on pianofortes?" There are great differences in sound, and there are even technical difficulties due to the fact that on a pianoforte, sounds decay much quicker than on a modern piano, so a passage with prolonged pressing of the sustain pedal will sound very different (and probably not as intended) if played on a modern piano compared to a pianoforte. Still, most agree that the expressivenes the modern piano allows outweights the less flexible sounds you get from pianofortes, and even more so from harpsichords. I admit that harpsichords often offer almost organ-like possibilities of registration, that way allowing to play with more colours. But this is fairly indirect and mechanical, compared to the more human, soulful ways a piano player can fine tune his/her playing.

The harpsichord is quite different from the piano in one very meaningful way. It's a plectrum instrument, meaning that the strings are plucked, rather than hit with a hammer, like the piano. You can touch the key on a harpsichord with varying degrees of force, but the sound it produces is always going to be the same volume. Playing baroque music on the piano allows for subtlety of sounds not possible on the harpsichord. The changes in playing Bach's music on the piano are interpretive. Instead of a mechanical, one sound fits all kind of playing, you have far more creative control at the piano. There is no hard rule that just because a piece of music was initially played on one instrument it can't be played upon another. Take any piece of music by J.S. Bach and you will find transcriptions for piano, orchestra, organ, guitar, cello, recorder, oboe, flute, etc. In fact, E. Power Biggs, the great organist, performed Scott Joplin's music on the harpsichord, and it sounded magnificent! Music is creative. Classical music isn't stodgy in this regard, either.

Hi. This really ought to be a comment and not an answer, but I was looking at Cimarosa’s Sonata in D minor as a practise piece. All the examples on YouTube play the piece as somewhat staccato. Do any of the people here happen to know if this is due to the sonata having been composed for the harpischord?