I don't think they misread the room at all. HP is pretty much at the top of the heap due to its corporate hardware installs and support contracts (which aren't going away any time soon). Their lower end stuff is all over the home office and small office markets. Their older stuff is used by much of the open source community. The number of folks who're going to switch to another manufacturer in disgust because of the tone of this marketing campaign will barely put a dent in their revenue streams for the next fiscal year, perhaps a fraction of a percentage point.

Incidentally, "we suck less than our competitors" is not a new marketing technique. It's probably the second oldest marketing technique.