DH & I ran into this problem last year, and didn't even realize it...
Toward the end of our trip, we decided that we really wanted to go back to 'Ohana a second time. We tried every morning at our hotel to get a reservation, with no luck. Well, two days before we were to leave, we were in MK and the line for Guest Relations seemed pretty small, so we figured it was worth a shot.
We were thrilled - the CM found something right away! He even offered us two different times to choose from! So, I took the little confirmation slip that they give you and when I went to put it away, I noticed that the ADR was for 3 people. We went back inside, because I didn't want to have a problem at the restaurant, and the same CM told us it was fine, to just tell them at the podium that there would only be two. He told us basically the same thing that you're reading here...a lot of times tables for 2 are unavailable, but tables for 3 are always easier to come by.