Well, I'll preface this with I rarely stay at RV Parks and when I do it's most likely for a clipper club rally...
If I see a 10-year rule on their website, I won't bother trying them. If they don't post the rule, but ask me the age of my rig, I'll tell them the truth.
I understand using the rule to eliminate run-down, broken clunkers and squatters, but I get tired of rules not being rules and instead subject to the whim of the person in front of you (or on the phone) at a given moment in time. I don't want to have to work that hard to give away my money.