OK...coming from someone who works in the restaurant industry...I think BOTH ways is practical. Having an ADR guarentees(sp?) you a spot. Which is nice...especially in a busy restaurant because you may run into traffic, an accident, flat tire, whatever the reason may be. Most restaurant hold the table for about 15-20 min past the time you're suppose to be there. If you don't show, then it goes to the next person available.
As far as walk-ups go, isn't that how most buffets places are...like Ponderosa, Home Town Buffet, or any other place in your area?? Some people may not get a chance to call and book a ressie or if a couple decided that they wanted to be spontaneous and go to WDW for a weekend/week, then they should be able to walk up to one of the table service(s) and see if anyone hasn't shown up for a ressie or see if there's any tables available. If it's two people, I don't see a problem. That's not takin away space for my family because there's 8 of us when we go. ANd I'm not saying the same for a family of 8 either..altough that might bug me a bit more..why...I just don't know.
It really shouldn't matter. I mean let's say for instance, Tony's restaurant at MK. Let's say that they have 75 tables in the whole place. Are you really going to be upset if they set aside 10 of their tables for walk-ups??

That's 65 tables of "guarenteed" tables they have for the whole day. That's about 90% bookings of ADR's.
I personally would love something like that. I'm doing a solo trip in Dec and I think it would be pretty cool if I treated my self to V&A and didn't have to make ressies. Maybe the rule should be parties of 4 or less don't have to have a ressie for walk ups. But if a family of 10 come bustin thru...then...sorry...you have to have a ressie...UNLESS another family the same or very close in size has cancelled or not shown up for their ressie.
OK...I'm done!! Thanks!!