From MSNBC MSFT could be down graded due to slow Vista adaption, that is a pretty big thing.
I believe Microsoft focused heavily on the new security items in their marketing of Vista but the value there is not catching on. To me, its the only real value of Vista.
The industry may be learning that security in new software products is now a given but unless you are marketing security products security is not something that can be used as they key item to sell a new product.
My guess is Windows 7 will have great security but it will be much less marketed — and Windows 7 will be fast, with great new value. If it does not what will people migrate to when their XP machines wear out?