I have both 3" and 4" binders, and I much prefer the 3" binders primarily because of less heft and bulk.

I can't answer directly if the 4" is more susceptible to breaking down,as it hasn't happened with the (newer) 4" Binders I have- but no doubt the stresses on a 4" are greater.
Speaking of binder stress, my 2011 Scott Classic Specialized catalogue binder is almost completely stripped off. I use it every day, and have dropped it a few times- and well, it is plainly worse for the wear.
