Hi Toofuzzy, What he said is that less often is better than more often, not that five years was best. His point is that fidgeting around too much is much more likely to make you lose money. He doesn't explain exactly why he chose quarterly. I'm guessing, that his thinking is like you said,
There are always limits to explanations in books, etc., because it can become a distraction to the key points trying to be made.