To build on Bigdragon's post about Ballmer not getting it, let's look at just what made Apple successful (yes, I know this isn't something Tom's audience wants to hear, but we need to look at reality here):
It all started with the iPod. A mere MP3 player! If it weren't for that, Apple wouldn't even be relevant right now! The iPod saved Apple from bankruptcy! Apple built off of that.
iPod touch + cell phone = iPhone.
iPod touch + growth hormone = iPad.
As for Microsoft, they weren't late to the tablet market. They've had tablets in the past, but they sucked at them. Now they're trying to copy Apple and are desperately trying to figure out just what is making Apple successful. Again, it's building off an already successful product.
Maybe they're trying to do that with Windows--building off of Windows to make their phone and tablet efforts successful. The problem? Apple didn't go back and change the iPod drastically to make the iPhone and iPad successful. Microsoft drastically changed Windows (8, RT) to fit their phone and tablet efforts, and it's not working all that well.
Then again, Windows as-is (i.e.: XP, 7) doesn't seem like a winning formula for tablets and phones either. Otherwise their previous efforts would have been successful (i.e.: Windows Mobile).
So really, the problem would be more than not having a base product that would be friendly to mobile devices...Microsoft is desperate. They're throwing things at the wall at this point, trying to see what sticks.