You're assuming that Apple has no process to distinguish between intentional fraudulent reviews coming from the developer in question, and random fraudulent reviews from others. But that assumption is not supported by any facts.
I would think its pretty easy to hire a click farm to blatantly post fake reviews to the app store. The worse the click farm is at covering their tracks the better if you're trying to get a competitor banned by Apple.
Dash was a popular app among developers who use Apple products I doubt the fake reviews would be needed. I wouldn't be surprised at all if this was caused by a third party.