i "buy" lotsa books through my kobo. they just all happen to be free
i partially bought my ereader to take advantage of all the 1.5 million (or whatever it is) free ebooks that you can get easily though kobo. i realise you can get them through other sources, and i do sometimes, but sometimes i like the simplicity of looking through the kobo store...easier than using the kobo browser a lot of the time.
I read a lot of classics, so being able to download free books whenever i have wifi is a huge bonus. don't know if/when i will actually buy ebooks, but for now, it's like a crazy good library.