Would be interesting to know if there were any s370 boards out there with onboard USB 2.0 by using a 3rd-party chip.
I really don't know whether these exist or not, but chances could actually be not that bad.
I never bothered to actually find out which ones (and if!) have USB 2.0, as (like stated by some others here) I saw no need for the extra speed, I barely ever noticed or missed it. Would probably be easier to add a separate 2.0 USB card anyway.
Perhaps a good way to look for such boards would be to find out which USB 2.0 chips were made during the late s370 motherboard production era, as those chips might have been used on those motherboards.