It's a perennial right that the Mouse bestows on his runners stemming from the days when the race programs were snail mailed in October. The mailing label was the race waiver and on it, your race number was included. Since going electronic, the Mouse has let us know about a month pre-race what our race numbers are. For all practical purposes, letting folks know what they bib numbers are is only a couple week longer than the TnT races. And, like you said, much earlier than most local races since the numbers are not known until the expo for most races.
The day waiver links are opened, the boards will be abuzz with guesses of corral placement (not released until the expo) and whether it is important to bring proof of time, etc. It's fun to read, but makes the last month crazy at runDisney as they are forced to field numerous questions. I think the RD would be better served to not release waivers as early. Just my 2 cents..
Oh, even as I write this, I have checked the waiver link area daily for the last week, just in case.