Most likely the explanation is a combination of many factors already discussed at length. Engine oil has been able to reduce friction for quite some time. Many examples exist that demonstrate an engine can run for some time without any oil remaining in the pan. Don't you remember the commercials for Castol as well as Nissan's VQ engine? Some of us have done this experiment accidentally.
If you're engine is run under normal conditions, the BMW recommendation is probably fine. Changing it early is insurance, nothing wrong with that if you are ok with consuming resources when not needed (don't worry, I change my oil more frequently as well). Economics definitely plays a role here as BMW's shift to longer intervals coinciding with their paying the bill is too coincidental to ignore. The likely reason for their shorter recommendation for their earlier cars was to help out the dealer network, you know, back scratching. Most people will still use a dealer to change the oil, convinced it's "necessary" to maintain their warranty. Go figure.
'11 X3 xdrive35i
'05 XC70 (family truckster)
'05 Sienna XLE LTD AWD (road tripper)
'06 330i MT, sport,premium (retired)