I can think of 1 problem with that, some old version are no longer around, ie, napster (til Dec when Roxio reopens the service - but will prolly use diff clients)
There exists plenty of places that host new versions though.
Most people who want new verson can upgrade via the program's built in upgrade option, OR go to a place such as CNet.com or tucows.com or zdnet.com or rocketdownloads.com, the list is endless.
But there are not many places that host old versions. Most that do are MAC based anyhow.