I have to agree that this approach is always going to cause problems to some extent. (I speak as one who bought a B+ a week before the Pi2 was unveiled!) On the one hand it's good marketing because people like (nice) surprises, but I'd hate to be a bulk-purchaser who'd just bought a truckload of Pi2s right now.
It's the way it works in the rest of the software and hardware industry. It's better to announce late than to announce something that isn't ready on the general availability date.
I mean, don't the Foundation think that maybe a better approach in future would to let the public know that *something* new is incoming, without giving away exactly what it's going to consist of? (There, a question finally lol.) Imagine how much fun you could have teasing all us slavering fanboysngirls...
Look at the complete foul up with the RPF 7" touch screen which was announced nearly two years before it was available. That made a massive dent in the Raspberry Pi Foundation's reputation and frankly made them look like a bunch of amateurs.
They can't win either way, but announcing closer to availability has better results for most folks. Their only problem now is stopping The Register doing their annoucements for them (a couple of days before the official announcement).