As a LFT who just got back from another trip to TVC, I can tell you why the ratings are down: The audience SUCKS!
That's an interesting hypothesis, but there are just two problems:
1. People don't watch the show just because the audience cheers. They watch because of the game, because of the host, because of the format. Assuming the crowd isn't napping, that's not really a factor.
2. The audience clearly isn't napping. Watching the show, I don't see that there's any tremendous drop in excitement. It may be that they're sweetening the applause a little more, but whether it's being manufactured or not, I'm still hearing the cheers. And the contestants that get on stage are at least as animated as they were with Bob, and in fact, they're a little MORE animated because they're grabbing Drew and jumping up and down in a manner that Bob tried to discourage out of concerns of self-preservation.
Frankly, if the audience isn't excited enough, that's a problem with Rich's warm up and Drew's interaction during breaks.