Possibly the fact that the Arrow had already appeared in Armada (...by the time WC3 was out), while the Hellcat could be 'iconic' to WC3? It's about the only explanation I can think of.Yeah! Isn't that strange? I wonder what could possibly have motivated the change.
...And then there's the WC4 intro, which shows Hellcats, while the WC4 novel replaces them with Arrows (though that can be discounted as a separate event).There was another strange Hellcat/Arrow substitution, too... the Kilrathi Saga replaces the Hellcat with the Arrow in one of the Victory Streak excerpts, doesn't it?