During 2001, *before* 9/11, the economy was going through a recession, and discounts that year were frequent. I believe that was the first year that "codes", those magic three and four-letter keys, became part of our vocabulary.
I remember this well, because I was scheduled to check in at the Yacht Club on 9/13/01, and I had a very good "code" discount of $169. (Ended up arriving on 9/14, in easily the most surreal WDW visit I've ever had.)
The problem with "local" codes that might appear in a metropolitan newspaper was that there is no more "local information" any more with the internet. So instead, the focus has shifted to pin codes, post cards, email specials, and passholder rates.
Before that, for a while, the popular thing was "upsell rates". But those again disappeared once the internet made them less of a secret.
I remember getting passholder rates as far back as '98, and I know I had a postcard rate for my second WDW visit, back in 1994.
So discount rates aren't new. I think what you're seeing is that discounts were plentiful during the 2001-2003 period, which is about the same time many people first got on the internet. Some may have gotten the impression that these had always been out there, and they were just now discovering them because of their net access.
The thing that led to discounts was probably the "Eisner building boom" of the late 80s and early 90s. Before that, Disney resort properties were the contemporary, Poly, Golf Resort/Disney Inn, Disney Village, and Ft Wilderness. The supply of rooms was much smaller, and selling out was the norm. At that time, there was often no need to discount rooms to get them filled.
So now, when the economy is buzzing along and travel is as high as its been in a long time, we figure to be in a natural cycle when there will be fewer room discounts. And the discounts we do see aren't as generous as we might have been used to.
In my case, it means I will probably end up in September keeping my Port Orleans
AAA rate, rather than getting a really great passholder rate at Wilderness Lodge or the Yacht Club, as I've been hoping for.