Google has a very different arrangement with the carriers than Apple does. Google does profit sharing of advertising income mades off of Android phones with certain Google functions embedded. Plus the phones themselves are much cheaper "retail" and don't have to be as heavily subsidized by dataplans saving more money.
It's in the carriers best interest to push Google phones. But, if you are on Verizon or AT&T your tethering days are getting numbered whichever platform you are on. Don't blame Apple for that now, and I won't blame Google for that later. That's all about penny pinching and controlling access on the carrier's end.
I generally understand your point...But another thing I forgot to mention was that Apple is used everywhere in the world, not just on US carriers.
The carriers in Europe didn't care about tethering when I was there last month, unlike their greedy US counterparts.
I used both Vodaphone and O2 from friends/family members while I was in the UK last month and can vouch for my statement about European carriers not caring about tethering being a fact.
Data is data to them.
If tethering isn't available either natively or at Apple's App store in Europe/Asia as well, then that means it's Apple that is mostly preventing it, and not necessarily the carriers?
US carriers certainly don't have any strange hold on the European or Asian market.
If we can hear from an European iPhone(stock only...not jailbreak) owner here that would be great as it would put both our suspicions to rest.
**EDIT**
I should add that "free tethering" was advertised on the Vodaphone and O2 plans I got to pick from. I didn't have to do any special hidden hack, jailbreaks, or anything like that. They are all freely advertised right there in the contract.
Check their websites.