I mean, seriously, of course there is such a word as 'deplane' -- just because one dislikes it doesn't mean it is not a valid word. I know what it means to deplane, and most English-speakers will also know it's meaning; it certainly seems to fit the criterion for being a word. Whether or not a word is a word is not limited to it's appearance in a certain edition of a specific dictionary! What a dull world it would be if language was static.
My point is that it's an unnecessary word. A word already exists to describe that concept - "disembark," as Macleod says. I'm all for new words to describe new concepts. Of course Chaucer didn't have a word for "internet," because he didn't need one. Likewise there's no need to create a new word to describe "disembark" when there's already a perfectly good word that serves the purpose. After seven years of living in the States, I have to say my impression wasn't that it was a dialectal difference, but rather ignorance of the fact that the word "disembark" exists at all.
Likewise, usage of such non-words as "winningest" on Nascar commentary makes me want to stab a bitch.
THis makes me think you've missed my point, though. Language doesn't evolve based just on necessity. Do you take such umbrage at every word that is redundant? Because if you do, I don't know how you can even stand to speak English -- with its dual Latin and Germanic roots, we have redundant words for nearly everything! And I don't think the specific example of 'deplane' is the result of ignorance of the word 'disembark,' it is more specified -- you can't deplane a boat. Adding to our language makes it richer, not poorer.
Winningest is also a word. It's even in the dictionary. It makes for a great adjetive: "Just flash them your winningest smile and be honest!" Why not just enjoy the evolution of language, and the inventiveness and playfulness it so often illustrates rather than getting annoyed by it?
Oh, I also love
it when people use 'literally' incorrectly, because the imagery is fucking hilarious.