Most of Gartner's income comes from serving as a sort of strategic IT help desk rather than from the publications you cite. They provide as much of a sanity check for enterprise/commercial IT decision making as a customer desires.

Individually, their experts are actually pretty knowledgeable IMHO more so on average than IT executives tend to be. There are many morons out there in decision making roles and there are many worse advisors than Gartner e.g. "advisors" who are unduly influenced by vendor payoffs (1st hand knowledge not supposition).