Not everyone is out to run a PB, or to get faster and faster.
Its about the motivation. I know many people that run half/maras in memory of folks they've lost solely to raise money.
The charity makes money, the runner gets a medal that says "Hey I did that half marathon and raised x for charity" and its a memento of the day they set out on that challenge and acheived it.
Unless you are in the elite, the only person you are ever running against is yourself or maybe a couple of mates you want to better. Maybe award the medals on personal accomplishment that you enter at the start of the race or on signup?
You choose the target you want to shoot for (PB/Sub 2/Sub 1.45/Finish) and only if you meet that target do you get a medal. Might be a bit more interesting, but nearly impossible to manage in a large field
Edited: 19/02/2013 at 13:35