The old console command "dumpmap" saves a map in Hexen format. Now that UDMF is around, it'd make more sense for it to use this format; since ZDoom now has several features that cannot be expressed in Hexen format.
Dumpmap was just used as a way to inspect the nodebuilder's output (via WinTex) before it was externalized to ZDBSP, so keeping pace with current features isn't particularly important.