The first article doesn't say much, the second leaves out an important fact: thick glaciers on Greenland don't percolate meltwater and are primarily geothermally heated. Their case might be made for the thin edges, but it's irrelevant for the bulk of the ice sheet.
The article indicates the observations were for a "equilibrium zone" of the Greenland ice sheet. As the ice sheet changes, I would also expect that the location and size of a zone thusly described would also change.