That may be why. HD utilizes a high volume low pressure oiling system due mainly to the fact that the crankshaft main and connecting rod bearings are not a babbitt type bearing that requires higher pressure to keep that barrier of oil between the bearing and crank. I don't think the 10 psi per 1000 rpm would be relative to an HD.
Mike

 

You are absolutely correct.. FWIW. I've got a gauge on a oil cooled 17 RK and with the stock early pump I get about 45 psi running down the road, 20 psi at hot idle. That's as good as my 131 ci TC with SnS pump. IMO don't even need that much pressure.. It's nice to have 15-20 psi at idle to keep the lifters pumped up but you really don't need much more running down the road. The only plain bearing in the bike is the plate side cam journal. The pinion side crank bearing really does not have any load and the oil to the crank has to be metered with an orifice to keep the crank from getting too much oil.

Add. Also main bearings are only splash fed.