IIRC, Kai's conclusion was that it's the aging.
+1. I think this hits the nail on the head. Otherwise the answers are pretty obvious as far as I can tell. To state what I think is fairly obvious, here it all is:
Use all fresh German ingredients
big yeast starter
constant fermentation temperature less than 50 F
racking is optional.
Near the end of fermentation, it wouldn't be a bad idea to do a diacetyl rest at 60-65 F, but only if there's diacetyl, otherwise skip it.
When fermentation is done, wait for the beer to clear, then keg or bottle right away, and then wait a good long 6 to 9 months in order to instill "that elusive German flavor". It will be good before then, but could be even better with age at least according to the Americans' palates.
I think that's pretty much all there is to it.
The only other question I have really is whether decoction makes a difference. Many people say no it doesn't. However, and this is only one data point: the best German lager that *I* ever made was triple decocted. Coincidence? I'm honestly not sure yet, and I am not jumping to any quick conclusions based on just my one data point. Many more experiments are needed before *I* make up *my* mind.