I know nothing on the matter, but it seems to me that it's a cultural difference. Americans are just more used to changing the oil often, so oil companies can sell them more oil even if they don't need it.

Found this http://www.autoblog.com/2009/02/24/oil-change-intervals/

"For years the accepted oil change interval (as per carmakers) had been every 3 months or 3000 miles, whichever comes first. And why was that? It was because oils of yesterday broke down when left in the crankcase environment for longer than the prescribed interval. The combination of heat, friction, and the oil oxidizing over time resulted in an unholy clothing of the engine's internal parts called sludge."

That's an absolutely insane number, and I have never heard of that (I have had cars for 20 years that always were 10k to 15k km intervals, and simply done on a yearly or 18 months service).

I have a tractor from 1939. The owners manual states that modern oils are much better than old oils and as a result practices of years past do not apply. (I don't recall the exact wording) If you ask collectors today there is a big debate on if it is safe to use modern detergent oils in those old tractors.

It's a difference in the oil used.

The standards for oil are tightly regulated in the EU.

The manufacturers are pretty picky with what oils they recommend for their cars too. I mean if I need a "fully synthetic 10W-30" for my car for example (from the manual) - and the brands are all global megacorps (Shell, Havoline, Mobil, Castrol etc). So with the tight spec and global brands surely I must be getting the same thing in the bottle here as one gets in the US?

Depends. VW has their own 'standards': 502.00, etc. Subaru theirs, and so on.

But many brands meet that spec. It's really only white label conventional bottles that don't.