Are you a very fast reader, or did you buy them to read later? I suspect people will buy books as they finish reading them... hence, comparing books sold on iPad/Kindle isn't indicative of anything.

I wonder if that is in part due to there being so much else to do on the iPad. When you buy a Kindle, I imagine you spend a bunch of time in the book store going, "Hmm...I'll grab this, and that, and that..."

Whereas on the iPad you have books to browse (Kindle store, Apple's store). Apps to download and play with. Music to listen to, videos to watch.