The MTBR Weight Weenies board gets ridiculous amounts of traffic. Road bikes must already be innately light enough... or just too easy?!

In road biking, it's relatively easy to calculate the impact of weight reduction. It's not a huge impact and, as you said, it's pretty easy to get the weight reduction. In MTBs, there's really no comparable way to determine the impact, and the bikes are a lot heavier. In road biking, people used to make claims like "these wheels gave me 2 mph during a long climb" but the math showed that this was the equivalent of a 50 lb. weight reduction, and their self-delusion was exposed. It's harder to debunk this sort of claim with MTBs, MTBs are heavier to start with, and so such statements can get made and everyone buys into it.

In MTB you're accelerating and braking far more often than in a crit for instance. It's also on bumpy terrain, at slow speeds (acceleration is greater,) and often has lots of climbing. 23lbs for a full suspension XC bike is pretty good for something that holds up. Still feels like a pig though compared to my road bikes.

Not some of the crits I've been in :rolleyes: ;)

In MTB you're accelerating and braking far more often than in a crit for instance.