If people know what *may* be coming in general terms, some will hold off and buy later some will buy now. Rumors do the same thing. Lack of information does the same thing. I personally don't want to get caught in the situation of just having bought a device only to find out that days later a new better (for me) device from the same manufacturer just launched.

There are examples of manufacturers releasing hardware roadmaps to give both developers and consumers some idea of what is coming (this despite competitors)

Intel including 2010
Intel
AMD info including 2011
AMD

Article about Samsung releasing 3 phones this year with LG comments
Samsung

So obviously, some companies are willing to entice customers and developers alike with some information about the future. It doesn't have to be detailed.