As Belle so wonderfully put above, indeed the rates are limited making that one reason we want to know ahead of time ASAP.
Second, it can be a problem (as I posted in another thread) applying a discount code if you don't know a few things - it normally can be done but there are exceptions (i.e. booking online cannot do it after the fact, even if you call, without a hassle of refunding/paying an additional deposit). And, depending on your budget, you may not be in the position to put down a larger deposit than you need (if you book early at a higher rate).
Finally, for many of us (and I think Belle and I are of similar mind on this) who live far away yet are AP holders we actually plan our trips around the discounts. If it weren't for AP discounts, I'd be a one-week a year person. Thankfully, because of the unlimited admission, resort, and Disney Dining card discounts (best $50 I ever spent!) I am able to make 3-4 trips a year. I have been tentatively planning a trip the second week of May, but I have done nothing but plan until now because I didn't know if rates would be available. If I had to pay full rack rate, I may not have come down at all (if the discounted rate is $74, that's just about my threshold for trips like this).
So, in a very long-winded, 'round-about answer, many of us "live" on these discounts, so their release is a momentous occasion. It allows us to finally solidify plans and for me helps me spend more time in the parks than I used to dream.
Hope that answered your question.
AEfx