The subtitle is a better way of framing it than the title, I think. Being accessible, all else being equal, isn't really inherently bad. For example, you can increase the accessibility of a poorly written physics textbook by just making the prose better.

The more interesting question they seem to be getting at is whether he's sacrificed something that was interesting about his writing out of a desire to increase accessibility. You could even just leave accessibility out of it and ask: are Neal Stephenson's most recent novels as interesting as his older ones, and if not, why not? I do think there's something to the hypothesis that he used to build these intricate, complex worlds with a lot of depth to them, and is doing so less in his more recent novels.

edit: Come to think of it, doing it accessibly sort of is his thing to begin with. I've heard Snow Crash described as a more-accessible reimagining/retelling of Gibson/Sterling style cyberpunk, which isn't too far off.