I would like to throw out this live grenade... With the trouser being the "traditional" garment on this side of the salt puddle, the tartan moved from the hip to the chest in the form of plaid flannel shirts. This is still the continuing of a "tartan" history even though it has moved up a bit. The American love of plaid has never diminished, it just moves around a lot. It is interesting that plaid boxer shorts outsell all other colours and designs together.
I've always loved wearing "plaid" flannel shirts (and yes, I have a fondness for plaid flannel boxer shorts too). I have noticed, though, that most of them are not actually a tartan pattern. They do not have the same sett in both directions. It's actually pretty rare to find anything on the American market that is truly the same pattern both ways. It's rarer still to find anything that's in a recognizable established tartan. Most are simply fashion patterns that have no significance.

It would be interesting to think of the American "plaid" pattern as a new form of American tartan wearing, but I don't think Americans as a whole see it that way or would ever adopt it in the same manner. Plaid is just one of many patterns worn, and falls in and out of fashion.

Sadly, if Americans have anything that would be comparable to the Scottish tartan, it's more likely to be designer logos. Be it Guess, Levi's, the Gap, Old Navy, sports emblems, etc., they use these logos as an identifier more than any pattern of colors.