I think the main thrust behind people's dislike of Hasbro is the idea that while the creative team is focused on the quality of the show, Hasbro, as a corporate entity, is focused on the revenue it brings in (both in ratings and in toy sales). Granted, that's true; they're a commercial enterprise and need to make money, so it seems odd to hate them for doing what they have to by nature.
In my experience, a lot of the dislike for Hasbro is almost of joking quality, about things like the low quality of the official toys and Princess Celestipink. I don't mind the playset cameos, since I'm really uninterested in them and they serve a narrative purpose as characters' houses, and a lot of the usual
Merchandise Driven stock tropes - like adding new characters to sell more toys - have been largely averted. In fact, a lot of the toy characters have never made appearances even as background ponies, as far as I know.
There has to be some element of executive control, though, both by nature and by the fact that 'Art of the Dress' exists. A panel I went to at CTCon 2011 pointed out that 'Art of the Dress' is directed at the creative team's superiors, especially the last verse - 'all we really like is what we know, gotta balance style with adherence', that sort of thing. If Hasbro wants to see true fan rage, though, all they have to do is start meddling for real with the creative team.