There are a lot of hints that Microsoft is backing away from this mistake and realizing that the desktop is still important to their bottom line.
I'm not sure that MS actually thought that the desktop was entirely unimportant, per se. Rather, it's my understanding that because they had a near-monopoly on the desktop market, they thought could get away with dicking about desktop users- most of whom had to use Windows anyway- by force-familiarising them with the Metro interface (whether or not it was appropriate for that purpose) so that when it came to tablets, they'd go for the one with the interface they were already familiar with... i.e. Windows-based ones.
Of course, MS were right to be worried about tablets. They've had a near-monopoly on the x86 desktop (and laptop) market for well over 20 years, and it was- and is- very unlikely that they could easily have been unseated from that position in the forseeable future. The biggest threat to MS's dominance is that the computing market itself undergoes a paradigm shift away from the traditional desktop model, not destroying their monopoly, but rendering what it covers less important. Which is exactly what's happening with tablets, and- to some extent- online apps.
Of course, whether forcing Metro on people was actually successful is open to question, but the motivation behind it sounds plausible. I don't think MS would throw away or ignore the desktop market simply for a chance of the tablet one, but I can certainly believe that they'd leverage their existing monopoly to stand a chance of competing in a tablet market that they're already miles behind the compeition in.