I agree some (okay, LOTS of) reviews are unhelpful and sometimes outright stupid, but giving *anyone* - especially the developer of the app - the ability to delete reviews is definitely a step in the WRONG direction:
What's to stop devs who make lousy apps (and there's plenty where that came from) from deleting perfectly honest reviews that aren't in their favour?
Review ratings like what Amazon has ("1 of 29 people found this review helpful") help to some extent, as would the ability to comment on a review.
But I fail to see the rationale behind needing a huge, complicated review review system because it doesn't take a genius to see that the "Not free? 1 Star" reviews don't make sense.
We're not robots to blindly average all ratings and think something that has a 2.5 star overall is a bad app. People really must learn to read through a few reviews before making a judgement.
(The official YouTube app being a great example of bad-app-turned-awesome that still looks pretty bad ratings-wise)