Ironically, I think, WMfantasy is even more medieval than WMMedieval -- in WMMedieval/WMA, the 'Bretonnians' must get down in the mud to win.
In WMf cavalry is extremely strong, and common folk with long-bows tend to be afterthoughts, especially if there's little terrain on the board.
The WMA limitations on commands (to max 3), and the limitation on consecutive rounds of combat tends to ensure that cavalry can get bogged down more easily, and the push of pike sometimes takes a while to resolve.
As well, WMA/WMM brings with it a larger range of troop types and abilities -- skirmishers, most notably, but also pike/phalanxes, maniples, warbands, etc. This adds tactical flavor to armies that are otherwise rather more homogeneous than the WMf armies -- only humans, after all.