Neat bit of UK language history, eh? In USA it would be White Out and everyone calls it that even if their particular bottle has "liquid paper" written on it. :-)
Too bad "PC" has become synonymous with "computer", though.
Let's compare nutty colloquialisms. How about "Q-Tip"? Is that what ya'll UKer's call "cotton balls on the end of little sticks for cleaning of ears and hard to reach gunk in computer keyboards"? Or is that in the realm of Mr. Sheen? :-)
Because it was the first popular brand , the name became synonymous with the product, hence all correction fluids became commonly known as tippex.