I shouldn't get involved since I don't remember which of you I usually agree with and which I usually fight with, but typo does stand for typographical error. And typo has become a word of its own, and typos is the plural of typo. Not a contraction.
Even if typo is jargon, it still has a regularly formed plural.
For example, someone might call a Stradavarius violin a Strad. The plural is Strads.
I don't know if this line from Kurt's sig was just a sig or meant to be an example: I get off on '57 Chevys. Another example.
Or maybe homer, which stands for home run. It's plural is homers.