Have they?
I thought that that was just a rumour. There were no quotes or anything in the articles that I read. So maybe they've complained privately, that's possible.
I guess it wasn't like a press release or anything, but it was reported by Bloomberg so I'd assume its true. I also remember reports that HTC and Microsoft were having some meetings and them saying 1080p was one of the things HTC was pushing for.
Anyway, I think Microsoft is going for an Apple-like strategy, essentially fixed specs that are updated yearly. The difference being in how they handle the non-premium market. Apple keep selling older devices, Microsoft releases new ones but all with consistent specs. Unfortunately, I don't know if we can expect them to stray from this.