I'd note that the Michelin page says it's a "reasonable guide of where to start experimenting," not a hard and fast rule.
On a hardtail bicycle, your tire pressure IS your suspension, so the optimum will vary according to road conditions, just as you'd adjust your ride height, preload and damping if you had full suspension. (And even with full suspension, optimum tire pressure varies according to conditions. That's why at a motor race, the tire people will post their recommended pressures.)
I'd also note that "recommended" tire pressures for automobiles have much more to do with comfort than efficiency. A lot of people (for unknown reasons ;)) don't like getting beat to death by the roads. The Michelin page also mentions comfort as one of the factors that went into their chart. You know how when you test drive a car at the dealer, if you buy the car, the first thing you do is check the tires and they'll be 5# low? Same idea.
There's a continuum between a plush ride and an efficient one, and every driver/rider has to make a decision as to where they like to be on that continuum. I like efficient. Other people might prefer plush.
Riding style has a lot to do with it, too. On my motos, for general street riding, I prefer fork springs that are very stiff for my weight. If I take the manufacturers' charts, add 30# to my weight and plug in that I'm an expert racer (which I most definitely am NOT :p), I'll come up with the spring rate that is most comfortable for me and gives me the best handling. But in the rear, I'm fine with a pretty soft shock spring, as long as I've got a ton of rebound damping dialed in. All of which points to I just load the front end pretty heavily. Other people might ride differently, with or without a motor.
I'll 'fess up to being a (retired) lawyer, but I think most of the others who've commented are not. ;) AFAIK, none of us here is a suspension engineer, so we're all just going from general knowledge and personal experience. And I'm still waiting for those articles about the laboratory tests... :cool:
And finally... who among us has had her tire pressure gauge professionally calibrated? :cool: Anyone who hasn't, which includes myself, is just going by a vague notion of what tire pressures she's actually running, which could be plus or minus 15# from indicated...
