I know that frictional losses would play a part in it, as it would in any radiator. The great surface area in a heater core would also have the same effect, just in a smaller area, though it would have less surface area than the tubing/fan setup.
As for pump head losses, that only seams to be a big problem in open systems like a bong. An enclosed system is given a boost against head loss by the syphon effect, and the weight of the water flowing down the opposite side of the system, so there's less head loss than one might think.
I had my heatercore in the basement under my desk, and the headloss was less than with the 5' bong sitting next to my desk. The pump's only inches from the same spot. That's also the same place I'd put the above posted system, because it is always 10-15C down there...year round.
'Sides, I'm looking at the BIG Eheim for my next pump, or maybe even dual Maxi-jet 1200's....haven't quite decided yet.