Not all Apple product announcements are “available today”, but they’re generally available either immediately or within a week or two, with a date certain, of the product announcement. I believe the 3rd-generation iPad that just came out was available about a week and a half after it was announced, for example. (In the U.S., at least. Some other countries had longer to wait.)
When Apple does make an announcement with a somewhat vague date, it’s a software release such as the upcoming Mountain Lion (”July”) or iOS 6 (”this fall”). These announcements also are made concurrent with making developer previews available, so it’s not truly vaporware but an advance announcement of a product with the lead time necessary to get the developers up to speed to make their products work on the updated OS.
Ummm.. the very first iPhone, was first shown by Steve Jobs to the public/press, a full SEVEN months before it was launched. This is the very first Microsoft tablet, and its coming out only four/five months after being shown to the public. Seems Microsoft is doing better(time-wise) than what Apple did with their iPhone announcement.