I dunno, never play spelunker, I'm sure that there are games that don't fit with the description I gave but over all the idea is there.
Clearly there isn't anything truly stopping devs from makin an game have a full list or if there is its not enforced. I know that most games with plats that are DL only seem to be full games released at retail somewhere or at least were released on psn due to funding.
I play a lil bit of everything on a lil bit of everything. Not changing this until we get a Viewtiful Joe 3 or HD collection of VJ 1&2 (started 8/14/12)
It's supposed to be based on a game's length/content, aka "full games". But it's clearly not consistent. Games like Trine and the sequel are very short and don't really offer anything outside of the main levels. And perhaps the best example, Plants vs Zombies. The version released on the PSN doesn't have a platinum trophy, and it even received a disc release later on. Yet the Vita version, which is download only and doesn't add many extra features compared to the PS3 version, has a platinum trophy.