Unfortunately Disney has to make it 10 per site based on camper capacity. Standard rooms have 2 queen beds which equal 4 people. My camper for instance sleeps 12, so in actuality I am being shorted on my capacity. It was a middle ground decision that Disney had to make I am sure based on ever expanding camper sizes.
I do see where you are coming from though. The simple fix is this: if you are not actually set up on your reserved site by midnight of first day then all benefits linked to your stay are suspended until you do setup. This would still allow for people who had an accident or breakdown to keep their benefits once they finally arrived.
As far as parking goes at campsites, the rule is 1 vehicle, Disney just needs to enforce it. When I stayed I couldn't get into my site because the second vehicle at the site across from me kept me from making my turn. Luckily a passing castmember simply went over and talked to them and the second vehicle was moved. I assume to the overflow lot as another person left the site on a golfcart and later returned with the driver.