This is the key!
Do you know why we like the convers of the DMG and MM and not the one in the PHB?
Do you know why we like the green dragon fight better?
It's about action.
Orcus in the MM is charging madly agaist a scared party off-camera.
The red dragon in the DMG is scrying on the PCs
The two guys in the PHB are... well... just standing there and looking "cool". It feels like they should be doing something
In fact, I don't think the problem is that there's only two PCs. It would be ok if there were two, exploring, fighting or whatever. (and no, the tiefling "shooting" rays is doesn't count, just look at his post)
And you know what? I think that the reason that we like WAR's art (well, me and the other guys that do, at least) is because it is always FULL of ACTION. Look at Eberron covers. Nearly all of WAR's art is action-loaded, except both PHB covers.