Right now, Amazon has an incredible way to market the kindle. It doesn't require a computer or anything from the owner (beyond an outlet to charge once or twice a week if you have EVDO on OR once or twice a month if you dont).
This is something that very few, if any other companies can claim. Not even cell phone companies can claim this - Verizon needs AT&T or Sprint or whoever in order to allow people to talk to everyone else.
Adding wifi support removes this claim - you're now dependent on the person's ISP (internet connection), router manufacturer (provides the wifi) as well as a few other misc things. That takes away from the simplicity of the device.
Amazon could provide both a wifi and an EVDO connection. Wifi chips probably are very cheap on scale these days.
If the EVDO connection is available in their area, great. Use that. But if it is not, users can figure out how to set up the wifi connection. They have to figure out how to set up the wifi connection in their notebooks anyway.
I am an international users from Italy, and I was very frustrated to learn that apple cannot open internationals markets not only for the ability to download content from everywhere, but also because it does not have the rights to sell 90% of the ebooks outside US.
