From DBWiki
The differences between WebBuy and PeerBuy have to do with how the files get to your computer.
When using WebBuy, you are downloading a zip file directly to your computer from the Bitmunk website. This zip file has all the individual files (songs, movies, etc) that you purchased contained in the zip file. This is useful if you are at someone else's computer or a public terminal and cannot access or install the Bitmunk Client software.
PeerBuy is the Bitmunk system which allows fans to sell an artist's work to another fan. The artist has set their base price, and Bitmunk ensures that the artist gets what compensation they want for each sale. In addition, the fan who is selling on the artist's behalf can add a small fee for their distribution service. If the seller is able to provide a faster upload, they might choose to increase their seller fee. A seller who cannot provide a fast upload might choose to lower their seller fee to compete with faster uploaders.