I am absolutely in love with all Steampunk costumers that I find at the cons. Especially with the release of the movie 9 last year, it's brought more fans into the genre. Considering some animes certainly have steampunk elements (Last Exile, Steamboy, Robot Carnival, The Count of Monte Cristo, ect..), I see no problem with it being cosplayed at conventions or even panels about it.
Probably my most favorite photo I shot at A-kon last weekend was a Steampunk version of the Mad Hatter (which, I saw plenty of Alice in Wonderland cosplayers as well, and I certainly don't see THEM being picked on, as they shouldn't be.)
(By the way, I am looking for this cosplayer XD If this is you, please PM me!)