"Bring to a boil, then lower the heat and simmer." Why?

[DanBlather]

@DSYoungEsq

That “very informative” website shows nothing except a bare definition that is not universally agreed upon. As is noted at Wikipedia (no, not definitive, but a good basic explanation), some chefs assert that temperatures as low as 180 F are simmering, but in general, water begins to simmer at 200 F, and I maintain that, for the average cook in a kitchen, your “simmering” water is probably at or very close to 100 C. It takes a great amount of precise control, usually absent with most average stoves and cookware, to get to where you notice the difference and can keep it that way indefinitely.

I have checked my thermometer for accuracy and I need to have a rolling boil for it to be 212 F. At simmer it is significantly lower. I am sure the water at the bottom of the pot where the bubbloe are forming is a boiling, but the rest of the pot is not. Also, meat is much tougher when cooked at boiling than at simmer.