If a faulty ethernet driver lets you compromise a laptop just by plugging it into a malicious network, that's a legitimate vulnerability, not really a case of "well, they had physical access".
USB may be customarily treated as more trusted than ethernet, but there are clearly still scenarios where untrusted people may be able to send you USB messages.
"Here, mind if I plug my video camera into your Firewire port to charge (and trawl through your ram and swapspace looking for any usernames and passwords)?"
I dunno - with USB debugging turned off, you can't do much to an Android device even if you can plug an arbitrary device into its USB port. There's a reason I make sure it's turned off every time I leave the house!
To some extent, sure, but we don't have to make it easy to get root access. Encryption on hard drives, removing the USB auto-play feature from windows, having to enter the PIN on a WP7 device before being able to deploy a developer app over USB, ect, are such examples that can make it considerably harder to get root access despite having the physical machine.
If a faulty ethernet driver lets you compromise a laptop just by plugging it into a malicious network, that's a legitimate vulnerability, not really a case of "well, they had physical access".
USB may be customarily treated as more trusted than ethernet, but there are clearly still scenarios where untrusted people may be able to send you USB messages.