What is the reason behind having to pay renewal fees for Domain names, when you 'Buy' the domain name. Surely it is therefore your property? Is there any way to buy a domain name outright without having to continually pay renewal fees?

The annual fee is a service fee. Running domain names is a costly process. While companies like Verisign and GoDaddy are operating with quite nice profits, there are many companies running domain names that find offering the services very costly. Charging a once off fee would probably require the initial fee to cost more than $100 as the domain registrar would have to insure themselves against all future costs and this would be a very risky gamble that could have the potential of domain registras going bankrupt if they underinsured. Imagine spending 30 years developing a website with millions of dollars only to find out you were at risk of losing the domain name because the registra underestimated the ongoing costs by $50 when you bought it 30 years earlier. Forecasting hundreds of years of expenses is a very risky thing to do as there is often unforseen expenses that are difficult to predict and the market is often not very respectful of the high costs associated with forecasting. If you want to buy the domain name outright and never pay annual fees, it is possible to set up a fund that reinvests most of it's profits within the fund and pays annual fees to domain names with the rest of the profits. If the fund is managed well then it should keep paying annual fees for at least the rest of your life and potentially hundreds of years. However, when you die you will no longer have authority over the fund and whoever inherits this authority may very well decide that they want to spend the money in another way.

Alas, unless you own the registry it is impossible to own a domain outright. You could, I suppose apply to ICANN for one of the new gtlds but that gets rather expensive.

You don't buy domain name, You REGISTER it for 1 yr. and further renew it if you want to hold it. Domain name is intangibles asset and it cant be BOUGHT and will be amortize with time.