In his defense, I suppose a certain amount of small material (including a few little rocks) would probably accumulate over time, hidden by the clover. So that part's kind of fair, I guess.

Just that, if you don't need to actually mow it, then what matters it? If I had to speculate, I'd guess that he was used to a lifetime of grass lawns, felt a comfort zone there, and was always a bit uneasy about the clover lawn. And yet, didn't feel up to arguing that with a certified Master Gardener while she was still alive.