Re: I do like Three.
Um... well obviously there is no difference between 1GB by one method and 1GB via another.
But that's not actually how it works... when you're watching a 10 minute video on your phone, it'll use less bandwidth than when you watch a 10 minute video on your computer. In most cases. Like on YouTube, where the bitrate/version served up on one isn't the same as the other.
Similarly, when you visit many web sites (perhaps a majority of the popular ones) on your phone, you'll get a mobile optimised version (using less bandwidth) than when you visit on your laptop.
The simple reality is that using services on your normal computer will pretty much use more bandwidth than the eqiv on a mobile (yes yes there are exceptions etc etc, but in the real world where the majority of the customers will be...) so it is a bigger issue.
In theory, if operators just gave you a fixed allowance it wouldn't matter how you used it, so the tethering issue would go away. In reality they give allowances beyond what is sustainable if everyone (or more accurately "enough") people used it, making that a problem again. If they give lower allowances they look uncompetitive and the other operators play the same silly game. Punters demand "unlimited" (well some do, normally the ones who are responsible for many of the reasons unlimited stops being unlimited because the spirit of the concept is pushed a bit too far).
And so we end up with this sort of mess.
Part of the issue is that as usual we've played rock bottom pricing games. We went from per "MB" charges to "unlimited" and "1GB for £2.00" madness. Operators would have been better off sticking at some flat rate (say £2/GB) and that I would think reasonable. They would make money, usage would be better paid for, and nobody would have need to worry about tether or not tether.
So the summary is, it's not actually 1GB vs 1GB, it's lower usage (mobile) vs higher usage (PC/mac/etc), coupled with stupid decisions by operators and the usual minority who use as much as possible "because they can" and then spoil it for everyone else.