As with everything, its simple.
Microsoft have known when Windows 8, Xbox update, Windows 8 tablet, are coming out, the tech press has known its around the beginning of november for a year or more. As they are doing loads to unify the platform, it makes very little sense to release WP8 months before all the rest of the Windows products, especially if they are all optimised to work best together.
Microsoft could have kept completely quiet about WP8 until mid october. Then released everything in a huge fanfare, with release dates, prices, carriers, etc.
The problem is the mobile market is soo big and fast moving, and has the huge enitity that is the iPhone, that keeping quiet would just have lost Microsoft tons of sales.
Microsoft could have told the world everything about WP8 back in June, where we found out most of the features. But if they had told us everything, what would we have to talk about? Add to that Android then has 6 months to copy any interesting features, meaning all the new stuff for WP8 is already available elsewhere.
I don't see that Microsoft have any choice, but to keep trickling out information, keep the press and fans talking about WP8, then at the last minute, do a HUGE presentation for Windows 8, Windows 8 Tablet, Xbox update, Windows Phone 8, and any other products they have.
I'm only expecting new features to be Windows 8 eco-system related, so not anything earth shattering for a phone, but when all the Windows stuff is put together it works better than the iOS system.