Well, stars should be a function of both expectations and service, so I don't think it's wrong for both a Michelin Star restaurant to be rated equal to a Subway.
They're probably measuring the wrong things. Maybe they should have something similar to the AirBnB / eBay ratings, which measure a lot of categories.
The 2 and 3 star complaints? Trivial crap.
"Sure the food is great, but other restaurants also have great food, 3 stars."
"There is this other restaurant on <other side of the country> that has food as good at this restaurant, and my meal was $30 cheaper!" (for a $200 meal)
"I had to call ahead to get reservations, they couldn't just seat me, 2 stars"
Crap like that ends up with Michelin Star rated restaurants having equal "star" ratings on Yelp as the local Subway.