You're going to get even less of a direct answer since the manufacturers often say basically nothing about the tubes they use. The LHT being listed as chromoly with double-butted main triangle tubes is vastly more specific than what you get with most of Trek's lineup.

If it means anything, the Trek 920 uses "100 series alpha aluminum", the same as on their entry-level 1-Series road bikes. It's sort of hard to infer anything from that, though.