As Mike states in his Old School Maintenance Schedule, he is merely repeating the maintenance schedule that BMW used to push before they had the 4 year/50,000 free maintenance program. Since the current selling model for BMW is to have buyer to lease a car for 3-4 years and then trade in on the latest model or update to a different/higher model, these buyers will never pay for maintenance and thus have no need for the Old School Maintenance Schedule. For some people, this is a great way to have a relatively new, maintenance-cost-free vehicle.
For people who buy their car with the intention of owning it for more than 3-4 years, or possibly 10 or more years, and want it to last 100,000-200,000 miles, then one might want to change the oil more often than the 15,000 miles now recommended by BMW based on their current sales model. These are most likely those that also buy a used BMW, probably out of warranty already, and want it to last another 5-10 years or more. Many of these people will also do their own maintenance at least relatively simple things like oil changes, brake fluid flushes, and brake pad and rotor replacement.
Mike also recommends proactively replacing parts are historically known to be weak or historically have a known service life before they fail to avoid more expensive maintenance costs when these parts do fail.
And a sample rate of one person is far from statistically significant.