Because ive never used the terrain extension in Horde
, and it was in part of testing the newer Modo Collada exporter.
However I tend to feel these days that terrain systems in general inheriantly introduce limitations derived from the normal 2d hightmaps. A well modelled geometry mesh can be just as optimised (if not more), with far better mesh density control not limiting you to defined grid resolution, you can also begin to introduce highly detailed areas in specific parts of your world without compromising the overall map design. As always theirs advantages & disadvantages, but either way it project dependant on the requirements.
Will have a fiddle around with the heightmaps later today for the terrain extension.