...but I haven't noticed it mentioned in any of the "popular" articles and sites I've noted:

How do you geo guys factor in the difference between Mars and Earth gravity? I would imagine that it would make big differences in the way erosion works, for instance.

Are there models?

Is there earth-based experimentation that has been brought to bear on the problem?

Or do you assume (for example) that roughly same-shaped channels imply similar things on Mars vs. Earth, regardless of gravity?

More differences should be caused by the vastly different atmospheric pressure. The differing atmospheric composition might have a miniscule effect. However atmospheric effects are much easier to simulate on earth than gravitational effects.