From responses to similar issues I've seen from the developers and general knowledge of the game development process, let me explain it to you:
Of course it would be nice if collars showed up. It would be great if every single piece of equipment had a unique model and tons of unique animations. There can always be MOAR of everything in a game like this. What developers have to do, once they have the core story arc complete and are satisfied with the game engine and the way the primary content plays, is prioritize the near-infinite list of added features, background content, etc. along with balance fixes, bug fixes and whatever originally planned content takes longer than expected (see: Shale).
So, the reason that collars aren't shown is the same reason that there are no cloaks, no [insert missing permutation of race/class/gender] NPC, and none of every other feature you can think of that is "missing" from the game. They didn't have time to get to it if they ever wanted to release the damn game.
At this point, I think balance and bug fixes are the main patching focus, and new content is constantly being worked on for DLC I'm sure, but I wouldn't expect random little graphical upgrades and niceties anytime soon unless some ambitious player figures out how to do it in a mod.
If this is your 1 and only complaint about the game, you must be thrilled. I have quite a long list, but this is still one of the best games I've played in a long time - only the games I love have this many tiny details I have a strong opinion on. If I don't like a game, there are usually a fairly small number of big reasons why I don't enjoy the gameplay and that's that. With Dragon Age, all my gripes are based on the fact that I love the game and want MOAR of all my favourite elements. Hopefully, as the toolset community takes off, we will start to see some proper content modules coming from 3rd parties. As much as I love DA:O, the idea of tons of quality content, with gameplay mods and balance changes to make it more of a 'hardcore' tactical RPG, would be 100x better. Even better would be if BW decided to make TOR a hardcore tactical pvp MMO, but that's a bit of a pipe dream