AFAIK feeding meters has been illegal for a while, but I have yet to hear of anyone being cited for it. This is nuts! Maybe if the meters were more reasonable people wouldn't do stuff like this...
Bear with me...
In some cases of abuse, like with NYC metro cards, there is a legitimate reason not to use a single metro card for a number of people (the limit is four I believe). The reason is because putting a large enough money on the metro card to accomodate those people automatically gives extra money as an incentive for large purchases.
But if you use this other people, you're technically ripping off the system, because those individual $2.50 cards wouldn't have gotten any extra percentage.
So in examples like the foregoing, I get why it's illegal to "share" money. But feeding parking meters has no such incentive anywhere, as far as I know. Why would it be illegal?
Because its about revenue. The cities want to give out tickets to prop up their bottom lines. Yes, there is a congestion and anti-car component but do not be fooled, its all about parking tickets.