No, what you are seeing is not a loophole. It's almost certainly ignorance on the part of the designer. The majority of designers are not as assiduous as you are. They didn't bother to check the terms and conditions, and they certainly didn't bother to contact Facebook, etc. for clarification. They just went ahead with the modified logos.
Of course, that doesn't mean they will "get fined in the future". They might well get away with it, if only because Facebook, etc. have bigger fish to fry.
But my advice to you would be not to risk it. Just use the correct, unmodified logos according to the terms of service. It's not as if modifying the logos would provide any substantial benefit to your client. And it would be very embarrasing to yourself if Facebook or one of the others did take action against you.