I agree Helz, it's absurd. If we did something like "FIAT (logo) are CRAP!" then ok, but what this site does helps Fiat and supports them, it would be nice to have a bit of support back. The cost to Fiat of their logo is so small it's negligible, they have so many lawyers that the £1k or so to do it privately is a joke.
The above isn't why they don't approve, they don't approve because they don't want to seem to be supported/support something they don't control for obvious reasons.
Getting your logo wherever possible is one of the first basic rules of marketing, at least Fiat see that enough that they let FF use it at the top.