How important is size?

[lukelightning]

(while strangely the trolls are only medium)

Trolls appear to be large because they are swollen with teh awesome.

 

[Cirex]

In the WarCraft D&D Game the tauren are indeed large (while strangely the trolls are only medium)

Edit: On a closer reading it says that tauren are an average 9f 7.5 feet tall while trolls are only 6 feet (with only a few exceptional trolls reaching 7 feet)

Are important NPCs considered large too? Because oh my, Jaina is sure tall at Mount Hyjal...