According to recent testing by Bicycle Quarterly the difference between a heavily constructed tire like Rivendell's "nifty-swifty" and a lightly constructed tire like the Grand Bois "Cypres" could be as much as eight hours over the course of P-B-P, for a 150 watt rider. And for the most part, lightly constructed tires offer more comfort than heavier tires. Apparently the light sidewalls flex more and absorb more shock.

Weight by itself isn't terribly critical to me, but it is to other people. They key for me is that light weight seems to go hand-in-hand with low rolling resistance, which is important to me.

True, but I didn't say anything about high pressure racing tires. I said "tires of construction essentially identical to racing tires, but wider."

Have you ridden a wide tire of lightweight racing construction? I'd guess that you are basing your comments on preconceptions rather than personal experience. In my experience, wide, lightweight tires sound and feel absolutely wonderful, whether they are old Clement del Mundo tubulars or modern Grand Bois Cypres clinchers. Nothing else seems to match the feel of that kind of tire, and it's not a subtle thing. Compared to the Panaracer Col de Vie or Rivendell Ruffy-Tuffy -- both 28-30mm tires that I've used extensively -- a lightweight tire feels absolutely wonderful and is well worth the trade-offs in reliablility and longevity, to me.

Regardless, you seem to be arguing against a thing because it does not suit your needs, while seemingly believing that your needs are the only valid ones around. That you don't want a wide, lightweight, comfortable, "performance" tire (that admittedly isn't as durable as a heavier tire) doesn't mean that nobody else does, or that they should not exist.