LoL will always have a fanbase because it's "casual friendly". And because people have put a bunch of money and time into it.
But DotA 2 will have a gigantic fanbase and a much bigger competitive scene if it delivers.
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http://28.media.tumblr.com/tumblr_lcb35gGx0t1qailr4o1_500.gif
http://www.megavideo.com/?v=57N0YAEJ