Of course each app/service/product is unique, which is what you're really getting at (and I agree).

However, stretching this to the point where someone attempts to claim that a given app has first-mover advantage for mobile-photo-apps-a-bit-like-polaroids-which-you-can-share-and-add-filters-to-etc-etc seems a little ridiculous.

Taken to this extreme, every startup (that is not a direct clone) can arguably have 'first-mover advantage' for their particular set of features.