Maybe Microsoft needs to get things close to done before announcing it, then it doesn't look like they take years and years for things to come to fruition, which they do. But with Apple they have a press conference, BAM new iPods. When
are they out? The next weekend. That's how you sell half a million phones in a month.
Microsoft announces something. When is it coming out? Well, we're only in beta 1 but we'll have a tech preview in 6 months, yada yada yada.
I think you really hit on something there. Part of it may be that Apple can get away with this practice due to the relatively closed nature of their platform. Also, Microsoft is still trying out this whole "transparency" thing...with mixed results...and they
have to try to make their software work a gazillion different hardware configurations. Sometimes an open hardware platform isn't always the best way to go.