Well, 20/40 and 20/60 are NOT considered bad vision. In fact, you can still drive without corrective lenses in my state if you have this vision (which I have 20/40 in one eye - much worse in the other, but am not required to wear glasses when I drive). It is possible that the difference in how your son sees is so slight, he doesn't want to or remember to wear his glasses.
2 of my children have profound vision imparment at nearly 20/500 and one has 20/300. They don't even get out of bed without their glasses - they cannot see without them.
Get a new eye doctor - one that isn't going to tell you your kid is blind at near normal vision and clearly wanted to sell you a pair of glasses. Also, is it your son or your daughter? Hard to tell . . .
Good luck!