Try this scenario: I use my phone to download bits of data from the Internet. The phone sends those bits to a program. The programs to send the bits to my computer. Sometimes I use a wireless connection, sometimes I use a USB cable... but in both cases, the bits end up on my computer. I use my computer to send bits to my phone over those same USB or wireless connections. The program on my phone takes those bits and sends them back to the Internet.
Question: Am I tethering?
If you said yes, you are wrong... all I did was download a file, mount my SDCard and copy it to my computer. Then I copied some other files to my phone and uploaded them to my Dropbox.
What's the difference between what I just described and tethering? Time and the program you're using to do it. There is nothing in the contract about what programs you're allowed to use (except maybe malicious programs). So that leaves time. How quickly does the transfer have to happen before it's considered tethering? If VZW truly cracked down on tethering and it went to court, they'd lose... and they know it. That's exactly why nobody's been sued.
the difference which you're leaving out is you can still transfer through usb in airplane mode and you can still transfer wirelessly without using 3g and just using wifi (also in airplane mode). When you use your 3g connection you're using verizons network, which you have to pay for. The reason no one has been sued is because that's a ridiculous and stupid waste of money. Far easier to just tier data.