When I booked for DM's last year the CM insisted I should add the note to all my reservations (we didn't - it's bad luck here to celebrate a birthday before the real date).
This year, different CM, same thing.
Seems to me like they're encouraging it.
It makes sense when you think about it. The free dessert may cost Disney a couple bucks (if that) but they're getting $80-$100 from that table. At character meals, the free dessert is a cupcake. How much can that possibly cost for them, 20 cents ? And you have to pay $20-a-pop for TS breakfast to get it, vs. $5 or $6 at CS.
Who's winning ?
Disney wants guests to eat all their meals on property and encouraging them to celebrate their birthdays/anniversaries for the whole trip must help.
Plus, you're less likely not to show up for a meal if you think something special's going to happen. Adults who are celebrating anniversaries are more likely to drink alcohol too.
And for guests on the
DDP (which, by the way, Disney is pushing big time right now, to the point where it's starting to bug me) the dessert's already been paid for anyway.