A lot of original ideas-- perhaps most good original ideas-- are initially conceived of as x of/for y. Plus it is a good tactic, which we actively encourage, for startups to describe themselves in those terms initially. It may not describe a startup perfectly, but it's the the most information you can convey in one sentence.
Airbnb itself described itself as "Ebay for space" during YC. Viaweb was "the Microsoft Word of Ecommerce." When we first thought of the idea of a web app, we thought of it (not merely described it, but thought of it) as using the browser as an xterm.
I should write an essay about this. This misconception is like some unkillable zombie idea.
http://www.thetimes.co.uk/tto/business/industries/technology...