Firstly, there are no sites that host files on the Gnutella network!!! The files you find are files shared by people like yourself, your next door neighbour & people from all over the world. IF you thought you were downlding from a site then it sounds to me like you have been to a scam site to get LimeWire. See
Membership? - **WARNING** - Download p2p Clients ONLY Thru Official Sites (click on link)
Yes most audio formats are shared but ... mp3 & m4a are the most popular because they take up far less space. Apple Lossless is equivalent to monkey/ape format which is lossless format. Apple Lossless is obvious by being m4a format but much higher than 320 kbps. Monkey of course has the extension of ape, aiff & wav files can be found also but all these lossless formats are more difficult to find. FLAC is another lossless format.
You can still use mp3 format to burn cd's (not mp3 disks.) Many people do.