So funny you said that, just last night my wife and I stopped by a local gas station for a cup of coffee and a big lifted 4x4 with huge mudders pulled into the handicapped space. Sure enough he had handicapped plates on it. We just shook our heads, if he can even climb into that thing he isn't as handicapped as most old people I know.
Handicapped people without obvious problems (a short list, not all-inclusive):
Chronic Obstructive Pulmonary Disease
Heart problems
Arthritis
Bad hips
Bad knees
Blindness
Amputee
Many more.
This does not excuse the fact that there are many that abuse the system so they can park up front.