Thanks to twitter and other social tools complaints now get amplified and travel quickly.
There always have been a lot of pain and complaints in windows, macos & linux development, in any case, but we didn't pay much attention to it as we do now.
Problem with Android fragmentation, on top of that, is the frustration that comes when you compare to the competing platform (iOS). I'm not saying iOS development doesn't have its own pains, but it looks tidy and simple compared to the Android ecosystem. If iOS wasn't there Android fragmentation would be accepted as the normal state of affairs.
It is a big deal? Well, it depends on what kind of app you are developing and how much you can get away with. For some developers screen resolution differences are not a big deal, but different processors, memory, etc... are. For others the opposite is true.