My post you quoted was a reply to junkieís claim that the air in pneumatic tires (theyíre properly named) isnít what holds the vehicle off the ground.
Youíre absolutely right that letting air out of tires helps you get around off-road. Itís the best and often _only_ way to get your roadgoing vehicle un-stuck from sand, because deflation causes the contact patch to grow in size and decrease in pressure, which is the only way to float back up on top of the sand.
One must remember to stay in context when considering this stuff. Moving out of context (eg. throwing disparate items into a comparison) will cause many people to mistakenly lose sight of what is being illustrated.
In your rock crawling example, you donít experience excessive heat build-up because youíre going too slow. Where youíll see heat build-up is (staying within a single context for clarity in this example) if you take that deflated-tire rock crawler and drive it down the freeway at 80. Thatíll heat those tires enough that youíll see it easily.