It's just part of the marketing. It's similar in other niches, but not usually to this extent. They cater to Mac fanboys who anxiously await even the rumor of a new product. They get hyped up about "X" product then buy it in droves. They also like to unveil fancy stuff to the public. The sole reason the iPhone was announced early was that the FCC makes their data public, so it was either Apple or the FCC who would have announced it first. Also, Steve Jobs is more or less the heart of the company and runs things in a very specific way.
Just take it with a grain of salt and enjoy it. It's kind of fun. I'm a Mac fan but not overly so...I can say it's kind of like watching movie trailers, it's fun to get excited about new things