Error checking can easily be added to udp for control data. Infact in IPv6 it's mandatory. At one moment you say udp will lose out, but we know tcp will back off on its reattempts exponentially based on the congestion window. Thus udp would win out. The argument wasn't that it was a significant impact, the argument is that they can cause interference.
But it's the driver of the NIC that manages its network packet queue! Then it uses a an interrupt to signal the OS that data is available or that the window is open for transmit. I'm totally aware there's a lot more to it, I do socket programming everyday.
