ios 4.0 may or may not run great on an iPhone 3G, but at least they have the ability to update now. The problem with Android, for me at least, is your at the mercy of the carriers and manufacturers for updates, and there is no guarantee that your phone will even be updated. I give you the HTC Aria as an example, released in June, and Foryo 2.2 is out for alot of devices but there is no guarantee the Aria will ever see 2.2 and its less than 6 months old. That is a problem.
That is a good point. BUT, you are at the mercy of Apple and only Apple. If SJ doesn't want your 3G to get multitasking, or your iPod Touch 2nd gen to get wallpaper, then you can't do anything about it. At least with Android there are more variables in play. And you have the choice. Remember, there's no guarantee Apple will let you have the latest and greatest improvements on your phone either.