Lots of ignorance out there..
Unfortunately the best forumite to explain the nuts and bolts of the differences between the modders creations and what Bethesda are able to do because he is a programmer, was recently perma banned by the moderatiors.
From what I gather though in basic terms there are some files and code groups that modders routinely change that have certain dependencies that aren't as straightforward to change on the console. It possibly creates issues with certification or patching or the file types concerned are encrypted possibly as part of PSN operation but regardless of reason it still does not excuse Bethesda's stance towards the PS3.