One complaint I read over and over on this board is about parents who bring overly tired, cranky children into restaurants.
Even now that he's 7, I find it very hard to predict what DS's schedule will be like on vacation. Will he be so excited he gets up really early, or will he be exhausted from the parks and sleep late? Will he take a nap midday or wear himself out in the pool? Now, at 7 he still does a pretty good job of behaving in a civilized manner when he's tired, but a few years ago that was a different story. We didn't happen to go to WDW when he was a toddler or preschooler, but if we had I guarantee that there would have been at least one meal where I would have decided for EVERYONE's benefit (including you if you'd been in the restaurant) that switching that meal to a nearby food court was a good idea.
I think that asking for deposits for very fancy places like California Grill or V and A is fine, but to ask families to commit 100% in advance to keeping their reservation at 50's primetime (just an example) is going to result in either far less families eating TS or more cranky children.
Just my opinion.