Well "arp9" was coined by G&G, so that's why you get those search results. You could try searching "9mm aeg" or "airsoft pcc aeg" and you'll probably get a larger selection of pistol caliber carbines and the like.
Honestly, doesn't look like there's much of a difference internally. Externally the 2.0 has a 7 inch hand guard vs. the 5 inch on the original. The 2.0 also comes with a slim handstop and the whole gun happens to be about 190g lighter than the original arp9. Unsurprisingly, the 2.0 is longer as well. I guess it just comes down to your preferences externally.