This is not correct, all 2.1 phones CAN be upgraded and most manufacturers DO offer upgrades for their phones though waiting time varies.From my readings it seems most Android 2.1 can not be upgraded to 2.2, as it seems the Manufacturers must makes changes for the Android upgrade to happen.........and most manufacturers will not
What exactly do you need the upgrades for? Upgrades won't add a front camera or a flash or gyroscopes and there are no restrictions on the apps in the Market, like "only for Android 2.2" or higher. Basically you will continue doing all the same things you do now on 2.1.
There are no special requirements for 2.3 either and here's the list of 2.3 unofficial roms
Holidays Update: AOSP Gingerbread Ported to Other Phones: Here’s Our Frequently Updated List | xda-developers
What is your budget, btw. Do you want to by the best Android phone ever or just a phone that can do all the same things but with less glamor?
LG Optimus One for 9,900 has Android 2.2 and is small and compact and is not slow either, the camera is 3 MP and there's not flash but if you are not into digital photography it's more than enough for sharing snaps you take with a phone.