Well, you have been sceptical to other things GW lately ad been forced to take it back, Phil. Hence why I think we really have 7th ed coming in. I were considering getting Stronghold assault, but now I do not know. Best to wait and see I think.
Remember, GW wants to spring suprises these days and keep a total lid on anything. What better way to prevent people from preparing, considering etc if you land the 7th ed 2 years ahead of schedule! And maybe they, for some reason, want to phase the releases of 40K and fantasy?
The books mentioned, well it may be that the profiles will not be in the rulebook, just the rules. So you would still need those books to use it fully but even if you do not have their profiles you wiill know the rules about facing them in battle.
Or, GW may have decided to cash in extra by selling the supplements despite making an early suprise release. After all, those who bought the supplements would still have to buy the rulebook. More money to GW and their books are not useless, the are filled with high value pretty pictures!
It makes good sense for a buisness who wants their customers to spend more money.
And maybe there is a need to show an increase in profit and fast. Well, what could have more potential to increase profit than the release of a new ed of 40K?