I feel like that was much more true in the past but the X925 was only spec'd 18 months ago(?) and you can buy it today (I'm using one since October). Intel and AMD also give lots of advance notice on new designs well ahead of anything you can buy. ARM is also moving towards providing completely integrated solutions, so customers like Samsung don't have to take only CPU core and fill in the blanks themselves. They'll probably only get better at shipping complete solutions faster.

Honestly, Apple is the strange one because they never discuss CPUs until they are available to buy in a product; they don't need to bother.