I can't speak to home values, but I can speak to math (btw, not a recipe for being cool in high school). The math behind the pre-approval that you received is horribly flawed: tell me your income, I'll tell you a property value.
That method breaks down when the market isn't a 1960's suburb with identical homes, identical tax bills, and rates rarely changing. That does not describe Chicago in 2010.
If you found a home at $290k rather than $280k, but the taxes are $4k instead of $5k, the $290k home is less expensive.
If your preapproval is 30 days old, a $290k home today is less expensive than $280k was a month ago since rates have gone down.
There are a lot of "ifs," but you can manage them if you know what they are. If you want to walk through a pre-approval that leaves you better off, drop me a line.