What percentage of board games are still in print 10 years later?
Very, very, very few.
And there are very few board games that get played as extensively as a RPG. I've played perhaps 200+ hours of Settlers of Catan, and 50+ hours of Ticket to Ride. Both those numbers are on the higher end of the scale, although there will be a few outliers with much, much more.
Meanwhile, just for D&D 4E, I would have played 1000+ hours.
Cheers!