If you're a Microsoft partner or customer, is it that significant to know the people in Redmond are going to release Office 15 and new versions of Exchange and SharePoint early next year? Or that the next version of the Windows Phone OS is coming in October this year?
If you know about these things now, will it be of any use to you? How? Why? Will you tell people not to buy a product because there's a new one due in 12 months time? Even if you did tell them, would they really wait a year? Don't think so.
On the whole, roadmaps really aren't that important. They're more of a comfort than anything else, a source of reassurance for customers and partners that a particular technology will continue to be updated and improved over x years.
It's only when a company suddenly changes the map that things get hairy. And you're not likely to see that in any leaked roadmap.
Personally, I think most companies should just publish their roadmaps. Sure, they might take a hit if a product ends up being delayed for some reason, but if they front up about it, customers and partners are unlikely to be that annoyed. Openness doesn't hurt anybody and I would venture to argue that, in this instance, Microsoft is unlikely to suffer any damage at all.
It's far worse if a company quietly updates a roadmap without informing customers and partners of a particular delay and then gets found out. Or drops a product altogether. Now, that's when the trouble really begins.
Roadmaps are just the same as maps, no one has problems with them unless they're wrong and they end up somewhere they didn't expect to be.