Well, if you don't ask you don't get. ;D ;D
I have seen cars offered on Freecycle, albeit the 'needs attention' variety.
I find that the wanted posts prompt me to think about the items I have stuffed in the shed and cupboards and consider if I still really need or want them, if I don't and someone else has a need - then why not.....
Like you though, I am sometimes a bit cynical about some of the requests. Like everything, Freecycle is bound to be exploited and the freely given items end up on places like ebay or Sunday's boot sale. I'm not going to let the mean behaviour of a minority prevent me from participating in things like Freecycle.