We agree that XC equipment is advancing.

I guess the issue is - for me - why are the pros so reluctant to move to FS, longer travel front suspension and disc brakes?

The answer is. . . because they don't have to. Many, if not all, XC courses don't demand FS and discs, so there is no benefit to switching. Since there is no benefit the additional weight is a penalty. So, hardtails, V-brakes and 63mm SIDs rule the World Cup and NORBA.

In contrast, DH courses have become much more difficult over the last several years as technology progressed. Course designers keep challenging the riders with harder, more technical terrain. Fifteen years ago DH was a race down a dirt road, which was appropriate given the bikes of the time - rigid forks, canti brakes.

XC racers are successfully making the switch to pavement, and the reason they are leaving is that there's money in road racing and XC is declining. NORBA stats show that there are 1/3 the number of XC races in the US this year than there were in 1996. XC will never die (I hope), but it needs a shot in the arm - at least in the US.