The key is not just having one, but using it. I was on Ski Doo for 6 years and all of those sleds had them....... was never good about putting them on! Now my Polaris donesn't have one, but now I am thinking about adding one!
I also rode Doo for years, never wore mine.
I wanted one on my Nytro.
And I'm glad I have one on my Polaris.
It can be pita, but usually my problem is I pull n pull n pull and then realize I don't have the tether in...
Snowmobiles should come stock w/ a tether, for the ~$15-25? it cost for one. The cost should be far cheaper for bulk I'd presume. Granted, the manufacture would probably increase the cost by 200$ to include a tether..