Apple is 'enjoying' the current marketplace. It's arguable that they're still holding the pole position in terms of 'perceived' market leadership (although we all know that's not to be the case).

As such, they will continue to announce products closer to the product's actual market availability dates. As they have many times in the past revealed the product on the same day it goes on sale on their outlets.

For many companies without ready product in a market where dominant competitors are already selling, they do need to publish future products today; to entice the customers to wait for said product and not spend their money on the competitor's offerings. (ie: blackberry playbook, etc).