I got the impression that Amazon has put in real effort on the Kindle and is likely to keep pushing it for a while. They know this is a big change in how people read, and they know it will take time to gather speed. I think keeping the Kindle at the top of their home page is part of that project.
Plus, I've bought more Amazon books in the 2 months since I got my Kindle than I did in the six months previous, and I'm trying to be restrained, and checking other vendors for non-DRMed versions first. I bet they are getting a significant jump in bookbuying volume from Kindle owners vs non-Kindle owners, and I expect it's to their advantage to add more Kindle owners (beyond just the $ for the Kindle).
So overall, I don't think it's that surprising.