Many of them are the result of court cases at least in Turkey which at least represents some semblance of democracy (until alas you actually read the details). This is the case of Richard Dawkins, an Oxford biologist who reviewed a book by Adnan Oktar about Islamic Creationist theory. Mr Dawkins who sits firmly in the Charles Darwin camp on the origin of man, criticised the content of Mr Oktar's book, with the result that Richard Dawkins Website was banned and no longer accessible from Turkey! You can read more on the story on their website here - unless you're in Turkey of course when you can't unless via proxy websites.
Lots more websites are banned in Turkey although the list changes quite a lot - all wordpress blogs, YouTube and many more usually on religious grounds and some political ones.
Proxy Websites - an Important Role
Fortunately you can protect against this blatent censorship and repression of free speech by using a proxy to access websites that are blocked by these ISPs. The reason is that generally speaking the websites are restricted via IP address.
So for instance when I try to access www.richarddawkins.net from the example above - the page will come up as 'not found' in Turkey because the ISP blocks that IP address. If I used a proxy to access that web site then it would probably get through because all the requests would be forwarded and returned via the proxy address. Of course proxy servers also get added to these 'internet blacklists' quite often but rarely are they that responsive.
There are other methods of blocking web sites which a normal proxy website won't help you with but the software I use also encrypts the entire connection so there is no visible content either.
Here's an illustration of how your surfing looks using one of the Identity Cloaker network of proxies. The same would happen if you were using an ordinary proxy except your connection wouldn't be encrypted and thus be in clear text (and it will probably be very slow). The main point is that the web server only sees the proxy server location and so your location is never revealed.
Any other uses for Proxy Websites?
On a lighter note using proxy websites has lots of other great advantages - basically you become an 'internet resident' of whichever country you wish. So if I'm in Turkey I'll select a Dutch proxy and I surf as a dutchman, when I'm in the US - I can pick a European proxy to allow me to access my favourite online casinos and poker sites.
Back in Europe I can access the fabulous Internet Radio station - the Pandora website by choosing a US proxy. It gives me choices and using a proxy to access websites means I am in control of what I visit not someone else. You also used to be able to access stuff like the BBC News from outside the UK however a simple proxy isn't normally enough now as they are being blocked by most media sites, a VPN still works though.
Of course there are many other uses like bypassing school Myspace restrictions, or surfing at work anonymously, or reading the CNN news whilst bypassing the Chinese firewall in Bejing but of course you shouldn't do these because it's naughty! Proxy Websites are simply a way for people to take control of their web surfing, they are a way to protect their privacy - in fact a proxy website is an important tool of free speech in an information age.