Darth Lefty 

The largest bike-store brands in the USA each have their own brand of tires. On hybrids, city bikes, lower end mountain bikes, and so on, the bikes most people own, and don't go on forums about, the manufacturers put armored tires. If I had to guess, most of these tires never get ridden enough to wear out before they dry out and crack. But if they do, a bike shop will have a replacement much like it. Your thesis that Americans prefer racing tires isn't borne out, and I think it's also based mostly on other users of this forum.

As for Marathons specifically... Marathons are a name brand that has no cachet here for the person who walks into a bike store looking for "just a bike that's not too expensive." So an OEM isn't going to use them when they can install something cheaper for no penalty. Schwalbe themselves have a cheaper tire that's just as thick as a Marathon but is made entirely of tread rubber instead of having the soft layer, as well as cheaper tires with other kinds of armor. In the aftermarket, there's a few problems here for Schwalbe. First, our remaining bike stores are gradually becoming one-brand or two-brand dealerships that will also sell the brand's tires. Years ago when I converted my MTB to a commuter I walked into a Specialized dealership and so I walked out with Nimbus Armadillos, because that's the tire they had in my size. Also, Schwalbe tires in other categories don't have as good a reputation as their other brand competitors, so a bike store might skip the brand entirely.