Martin switched to heavier, non-scalloped top braces and moved the X-brace an extra half inch from the soundhole in the 1950's because so many people were using heavier gauge strings on their dreadnoughts exclusively. Repeated use of these heavier gauge strings, with their extra tension, would, over time, produce a "bubbling" behind the bridge, which, over time, could lead to problems developing with the bridge pad or nearby braces. The HD series attempted to copy the beloved pre-war Martin D-28 -- not just with herringbone trim, but with scalloped braces and an X-brace shifted forward to its original position. Therefore, consistent use of heavier gauge strings on these guitars
could (not
will) result in similar problems.
The best way to get around this is to use a set of light gauge strings every once in awhile to place less tension on the top. You don't have to do it all the time -- just every third string change or so.
It's a lot cheaper than buying a new guitar.
