The problem is that newer generations of smartphones were a direct competitor to RIM's flagship product, but mobile platforms as a whole are not direct competitors to traditional PCs, and it's not clear at this point that they'll become competitors.
PCs and mobile devices have overlapping functionality, but the use cases and contexts in which that functionality is applied are very different.
By conflating the two markets together, and allowing (poorly-conceived, IMO) product strategies for mobile devices to spill over into their flagship PC software products, MS has made a very serious error.
Isn't that pretty much the attitude that RIM had as well? This is not a successful strategy when you have to compete with a new class of devices.