I don't deny the numbers are there, but if you're making an advertising strategy based on mobile safari, you might want to make sure the websites are in order and your mobile conversion process is near perfect before proceeding with that. Also, these reports tend to not be similar data to what we actually see on dealership websites. I will have to confirm, but I know that most of our clients focus a heavy portion of their advertising on desktop browsers intentionally.
Agreed you need to have a mobile-ready (responsive/adaptive) website, but that is standard procedure in 2015. If you have a dealer site that isn't mobile-ready, you are already far behind the curve.
I have NADA data showing the average dealership website receives >39% of their traffic from mobile devices. It rises every quarter.
So 40% Safari usage with 40% of traffic is a significant number. Definitely worth strategizing for.