Here's the scoop, straight from the horse's mouth, as it were...
This new rule applies to all weddings BOOKED after Oct. 1, 2008 (not weddings that
occur after Oct. 1,
2009).
So if you book Sept. 30, 2008 for Sept. 30, 2009, you fall under the
old rule. If you book Oct. 1, 2008 for, say, June 1, 2009, you fall under the
new rule.
It applies to all in-park events, including dessert parties, rehearsal dinners, etc. This was not previously a DFTW rule, but it has been a rule throughout the Walt Disney Co.'s theme parks division since the (Two) Year(s) of a Million Dreams promotion began winding down.
The new rule came down from the very tippy top of the Walt Disney Co.'s corporate structure (well, OK, maybe not Bob Iger level

) so that Disney can better control the images of the theme parks, characters and classic Disney icons (e.g., Cinderella Castle, Spaceship Earth). Which means the change was not made by DFTW to make in-park weddings less popular with couples or to boost flagging interest in using Disney Photographic Services.
If having an outside photog at your in-park wedding is important to you and you can contract before Oct. 1, 2008, sign that baby as soon as you can.