HOA are awful, my parents had all sorts of issues with the one in the neighborhood behind them. Despite them never signing a contract, anything being in the deed, and the fact they lived on a county road, they tried to force them the join and even threatened to put a lean on the property. They fought it, and obviously won because there was no basis for the HOA's claim, but still it was a huge pain.
About the topic at hand though, I wouldn't want to live next to a bunch of pick-ups. One in the driveway is fine as long as it isn't a clunker, but still I'd rather not have a bunch of work vehicles next to my house. Our neighbor has a Chevy truck that probably ran him $50k plus and looks nicer than some of the houses on the street, so I'm OK with that, but I wouldn't want to look at some 1970's rust bucket. Also they probably should have read the rules before buying anything, it's the parent's and kid's fault they bought something that broke the rules they agreed to.