What are the main differences between  Adblock Plus and Adblock?

AdBlock (http://en.wikipedia.org/wiki/AdBlock_(Chrome)) is completely unrelated to the http://en.wikipedia.org/wiki/Adblock_Plus (which is available for both Chrome and Firefox), except that the author of the (Chrome-specific) AdBlock was inspired by Adblock Plus. As of today (July 5, 2013) they both seem to block YouTube commercials (which I know has been a difference between them in the past). Some very quick-and-dirty testing on my part seem to reveal that both the extensions have about the same memory footprint and function. (I basically checked one web page with a banner, and one YouTube video with commercial; both ads were blocked by both extensions. And they both took the same amount of RAM to do so, when checking with Chrome's Task Manager [Shift+Esc].) However all the reviews I can find comparing the two (like “http://www.freewaregenius.com/adblock-v-adblock-plus-two-chrome-extensions-compared/”) all seem kinda old and outdated so I can't really offer any better information here. – I basically only wanted to refute Gary Rowe’s answer, which may be an accurate description of how Adblock Plus started, but it does not answer the question of what the differences are between the Chrome extensions AdBlock and Adblock Plus.

Despite the confusingly similar names, they are completely unrelated  projects. On the surface, these projects have  different approaches but the resulting products are roughly comparable.  But in the background, there are tons of things to worry about in regards to Adblock and how it treats privacy and open-source matters. Wladimir Palant writes on https://palant.de/2014/07/29/which-is-better-adblock-or-adblock-plus: "AdBlock covertly moved from an open development model towards hiding  changes from its users. Users were neither informed about that decision  nor the reasons behind it. The source code archives are only left around  to keep pretending that AdBlock is still an open source project, these  are hard to find and the project owners are clearly hoping that nobody  will be able to extract the individual changes from them."