I'm a Brit ex-pat in the US and I travel on United almost exclusively to the tune of about 175k actual flight miles per year.
I fly with United because, while the fleet is somewhat old, and the service spotty at the best of times, the 'deal' with them (and many US carriers) is that they reward your loyalty through programmatic and complimentary upgrades. That is the expectation set forth, so it's not unreasonable to have a certain expectation in this regard, in fact, the FF program is really structured around this.
I can say in my experience, that the upgrade situation is not a 'free for all' United actually has a very organized way of managing upgrades, by ticket booking class, FF status and availability. The upgrade list is publically shown on monitors at most gates and is controlled by the booking system for the most part.
Additionally, I think a lot of people in Europe forget that the distances involved for everyday business and leisure travel are far greater than central Europe, therefore travel is signficantly more expensive. For instance, a 'daily' hop that I take from San Fran to Seattle, all in a days business, is 1600 miles return and at the very lowest $300, but usually $400-550 in cattle. This adds up quickly, to spending $15, $20 or even $25k annually domestically, therefore, the expectation is that for my loyalty I will be entitled to 'Unlimited Domestic Upgrades' per the criteria I listed above, which is the reason I continue to give them my money.
Now, having said that,
International flights are totally different. In order to be upgraded for Y->C or from C -> F you must have a suitable vehicle:
1. Pay the fare
2. Book an eligible fare and use one of the 6 systemwide upgrades you receive as a 1k member of the FF program
3. Book a reward ticket in that cabin with miles
4. Pay miles and money (similar to the above)
5. Pay an offered 'upgrade fee' ranging from several hundred to several thousand dollars, just like BA does from E+
There are no freebies. The only way to get from C to A is as listed. Even then, the priority is exactly as other carries internationally, ticket price, then status etc.
I'm bemused by the 'Seppo bashing' on the thread, somebody mentioned Asian airlines - having flown multiple transpac segments on a variety of Star Alliance flights, I can certainly tell you that 'operation upgrades' are almost unheard of - Singapore Airlines will fly you in the class you booked, for example, nothing more and nothing less.