Hot Water Tank limit switch tripping, but not over heating?
That limit is part of the Flammable Vapor Ignition-Resistant (FVIR) feature, which is required on all modern water heaters (since July 2003).  This particular limit, is designed to detect when there's a problem with inadequate combustion air.  

Causes of inadequate combination air include, but are not limited to:


Explosion of combustible vapors that have seeped into the combustion chamber.
Inadequate venting.
Inadequate makeup air.
Buildup of lint, dust, dirt, or oil on the screen.


Make sure you're not storing anything that could cause flammable vapors to be near the heater (gasoline, etc.).

Make sure the exhaust vent is sized properly, and is not blocked or obstructed.  

Make sure there's an adequate source of makeup air.

Make sure the lint, dust, and oil screens clean.

This is a fairly modern safety system, so it's no surprise that the old heaters didn't have the same problem.