Yea only makes since they had to compress it from a blueray to a file under 10 gigs
I don't think there is a file limit, Ratchet & Clank All 4 One is a 14GB download...
No you're not imagining. I've tested it. I find this a VERY questionable practice by Playstation. I bought Dead Space 2, having played it through many times on disc when it came out- and the PSN version is missing the final layer of graphics detail. It looks like the shader/detail quality is LESS on PSN downloads. I noticed that games that are BIG disc games look way worse when downloaded, I hope PS4 is different. I've bought a few games that I've felt a little ripped off on. Sleeping Dogs being the latest (it was free for PS Plus, but I pay for that).
Anyway, I'm sure it varies from game to game and publisher to publisher, but yes, PSN games are missing a level of detail.
I'll be getting the Last of Us on disc for sure.