Take your point about parents with kids not being near entrance, but surely you are not saying that disabled spaces should located away fronthe entrances, are you!
If you are, I'll bet that you have never pushed a wheel chair much, particularly with a disabled adult in the seat.
Also you will find that the disabled spaces are not wider , its just the parents with kids spaces that are wider, so that they can get the young children out in their carry cots etc.