Quoting WC3 is pointless. I seriously doubt that Blizzard (hell, anyone for that matter) can see so far into far into the future that they can maintain a storyline for 5 years without any plot-holes. Most 30 minute television shows cant hold a plot without holes in the storyline.
That being said, revenants are elementals, and Frostmourne was guarded by Death revenants. Death Revenant further implies a connection to old gods, especially yogg'saron. If that's the case, then as far as I'm concerned, the Death Revenant would encourage Arthas to take the sword, seeing as it would encourage a Burning Legion invasion, and the Old Gods have been known to incite Burning Legion attacks. Seems like a major inconsistency, and thus a plothole to me.
Anyways, my point is that i don't think it is a good idea to rely on blizzard for a consistent story, especially when you go as far back as WC3, and then try to discern meanings from the fact that Frostmourne was guarded by elementals. Blizzard is fallible, and a perfect storyline that has been prolonged as long as it has is beyond unreasonable.