Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple Release Apps Enhanced for OSX Lion Section in Mac App Store –
A new category has hit the Mac App Store called “Apps Enhanced for OSX Lion” You guessed correct its an section released for all Apps in which are enhanced for OSX Lion. The section has around 50 applications altogether and its good again to see Apple putting third party apps with in the top few rows.