Well, admittedly, going to a bar to "look around" is probably unique to Oga's - and seems fairly reasonable to me, considering that it's meant to be an attraction in and of itself. It's one of the draws mentioned on the WDW website as a reason to visit SWGE, so of course people will want to see it - and not everyone will want to drink.
As far as how many take up space without ordering in an average bar - I would guess that almost all college or sports bars sometimes have 1 or 2 people in a big group that don't order anything. I'm not a big drinker and I was often the guy that didn't order anything when hanging out at a bar in college. And I wasn't usually the only one.