I suppose going to war with Valve would have been pretty bad PR. Still, Valve was forced to change a bunch of Dota characters' names and visuals so as to not infringe on Blizzard's IP.

Examples: Windrunner changed to "Windranger"; Pudge made to look less like a Warcraft "abomination"-style creature; Skeleton King renamed and remodeled to "Wraith King".