Actually the buy link depend on the user nation, so for example here in Italy I see also links to the local online shops where I often buy, in addition to Amazon.UK.
Book reviews are an interesting part of aNobii, but not the only one. I for one find very useful to track what some of my friends (or "neighbors", line aNobii calls simple contacts) are reading (you can also set up an RSS feed), or have read in the past, or giving a look to the libraries of complete strangers that happen to share a similar taste for book.
Bye!