Never realised this spelling mistake was such a thing but now I notice it all the time!
I've been living in Bogotá for a few months and I only realised I was spelling Colombia wrong a couple of months in - pretty embarrassing.
I now notice many if not most of my English-speaking friends make the same mistake when emailing/facebooking/whatsapping me and I try to correct them as I go.
It appears Columbia is a reflex spelling of the sound of the word - I'm from the UK so haven't had that much exposure to the use of the word for the NY University, so I don't think that's the explanation in my case.
Someone should make a website for this along the lines of amispellingcolumbiacorrectly.com -> NO to spread the word ;-)