They're now saying that his helmet was cracked open, and they estimate that he was doing something around 50mph at the time of the accident (which is extremely fast for recreational skiing). There's also been photos and video in the media of the apparent area in which he was skiing. It's absolutely littered with rocks and outcrops.
It goes without saying that I wish him well, and wish for a full recovery (as I would for anyone - famous or not - who received such injuries). But I also have the opinion that an experienced and highly competent skier (as he was), who elected to ski at such apparent speed through such dangerous terrain, is electing to take a significant risk with his wellbeing (and his life). If he didn't want to put his life and health in anywhere near as much potential danger, he should have been skiing slower, or skiing fast on prepared slopes. It was his decision to make.
Skiiing is just a dangerous sport even if you take all reasonable precautions. While I was waiting to have my ankle x-rayed after a tumble (my fault, going far too fast down a mogul field on a pair of ski boards - minor leg break), a woman was brought in with a suspected broken neck. She was skiing on piste with due care and attention and an idiot on a snowboard crashed into her.
As it turned out, it was "only" a pair of broken collar bones and a few broken ribs.