I'm relatively new to snow biking -- just this season. Been riding sleds since about 1998, all makes and models.
I think the big difference is just due to the R&D. It used to be that you had to work on sleds all the time, set them up, make adjustments, etc. We are now at a time where new, manufactured sleds are ready to go (Mostly!) and awesome right from the dealer. If you buy a new sled, you'd probably get 2K-3K trouble free miles with relatively no maintenance (belts, oil, etc.)
The bikes are still in the infancy stage. It's basically people -- a lot of whom are on this forum -- taking existing dirt bike technology and adapting it to/for snow riding. Which means there are going to be hiccups and a lot of different setups, etc. And with no real snowbike manufacturer currently existing, there is no company R&D money being poured into development.
I purposely bought mine from one of the few dealers that builds snow bikes themselves. They are a motorcycle dealer, not snowmobile. I just wanted something that was already set -up so that I wouldn't have to go through all that. And I was willing to pay for it.
I've loved the bike this season -- every ride has been extremely fun and challenging. I've also learned something, or many things, every ride. Still have the snowmobiles, still have fun on them too, and don't plan on selling them. But, I'd say I prefer the bike at this point. Especially in any conditions that aren't tits deep powder.