Yeah, but trees don't fly at you at 30+ mph with no intention of stopping. In my experience, they are fairly stationary. 
That is 100% the point!
I actually agree with Josh about crowded groomers and safety (hence why I rarely do the VT Saturday thing)...I AM a low-skier density snob!
It is not that catastrophic injuries don't occur off-piste (of course they do!), it is that If someone hits a tree, or eats it on a mogul, it is 100% their fault and is the result of choices they made. And by that I don't mean that I have no sympathy for the injured or that I am above eating wood while skiing trees myself, BUT, off-piste injuries are the results of personal choices and conscious actions--If I hit a tree, I got no one to blame but myself and my skiing (or lack there of) and ignoring of the potential risks (or just deciding to accept the potential risks) or my failure to ski under control and with due regard.
On a crowded groomer, most injuries are the result of skier to skier collisions, and typically in those injuries, there is one very responsible party (who was skiing out of control or without due regard for others) and one who was an innocent by-skier. And, from my own 7 years on a ski patrol, I will say that the vast majority of injuries I have seen are on groomers (or people who lost control on a groomer and ended up off-piste!).
To LP's comments on mountain biking: I am, to be frank, a very good mountain biker. And, I only ride in the woods not on the road- I quit road riding for the same reason as I avoid skiing groomers on a Saturday in VT--the uncontrollable and accountable recklessness of others is too great a risk. Yep, I've spit gravel and kissed boulders mountain riding...and each and every time it was the result of something I did, or chose to do and no one else was to blame. But I know too many folks who have had catastrophic collisions (and harassment) with reckless vehicles. Somewhere out there every mountain biker has a date with a broken wrist and a separated shoulder, but you are not going to cash it in mountain biking and if you do get hurt, it's your fault and the result of choices you made and actions you took...I can't say that with road riding. I feel the same way with crowded groomers.
Dan, my home mountain (Berkshire East) is similar to Waterville: Racers dominate the slopes, skier density is very low and skier ability is high (in fact, the only place I have skied where I see a higher average level of skier is Mad River Glen mid week). And therefore, a Day on the groomers can be pretty good (even on a Saturday). I am used to skiing at mach speed on groomers, but would never ski that way north of Brattleboro on a weekend. I definitely get a nervous feeling skiing with the crowds (when my kids were learning to ski I had a number of times people collided with my children at Mount Snow and Stratton).
As a parting comment, my wife learned to get comfortable skiing trees to get away from the uncomfortable and dangerous crowded groomers of Southern, VT.