Buckeye, I agree with you to a point on your suggestions; however, while I like two of the three advancing (Tom an exception, but am OK with him), I have to admit that all three are stronger long term in the realm of a Las Vegas act should they be able to carry it beyond the opening act for a Vegas show.
Here are the reasons for the suggestions you made that I can see why they ended up out:
Dittleman - he had some good tricks; however, most of us could figure the sleight of hand that makes him a mentalist more than a psychic (those tiny details that you see Patrick Jane figure out in people on "The Mentalist"). When observers can catch this, there is a problem with the act, and additionally it's a harder act to do a true Las Vegas show long term.
The Scott Brothers - I liked their uniqueness, but they shot themselves in the foot a bit with their "vote for us" or arguing with the judges (all I heard from my parents was that they did something that wasn't popular). They also can't - just as the duo - hold a Vegas audience long term.
Rebecca & Donovan - I too was sad this team lost out; however, long term it's the same problem as far as a Vegas show - at least solo. That said, this does open up the door for them doing several Cirque shows, which might love having a husband wife duo who know each other's strengths/weaknesses that will allow them to try various new tricks. I could see this group as another Evancho in that reason.
Academy of Villains - they didn't have a chance thanks to being on the same night as overhyped Turf and a YouTube act. I do think this performance as better though, and they didn't get eliminated by being a bad act, just being on a night of strong performances.
Todd Oliver - good idea, but I think long term it's hard to have just the one dog for the sketches. He can expand it similar to Jeff Dunham; however, as it was just him and the little dog... I don't think it was as strong of a Vegas show.
Of course, we also vote for favorite act not just best - this case I think it was a bit of both, and it was just a curse that only three could move on. Personally, I think R&D and Oliver would've been the other two acts going by this analysis - you CAN expand their acts.