It's not about volume of recoil, it's about type of recoil. "Springer-rated" scopes require double bracing, since a spring-piston air-rifle has two-way recoil. That is, it has a hard lurch at the start of the firing sequence when the pison is released, and all that weight lunges forward, and then it has the second cycle when the piston slams to a stop on the column of trapped air at the front of the compression tube, and the piston rebounds slightly.
Shoot a 12 ft/lb springer with hearing protection on sometime, and you can feel all the mechanical stuff going on inside it...it's "ka-choinggggggg".
If you put your average rifle scope on a springer, it'll usually be junk in short order.