This game takes place 200 years (or is it 300? I forget, but either way its a while) in the future from Oblivion. And as an archeology major I'm sure guns would have been developed by this time. I'm not saying guns should be in the game. But it is a very plausible scenario. If done right I honestly could see it. As time progresses, technology changes, that's how the world works, at some point in the time line there will be more advanced technology, maybe not this game but eventually.
Those two hundred years were kinda Dark Age-ish though. Ya know, no ruler, government trying to hold together, and to finish it off we're in a part of the world that isn't that big on tech. I'm not saying tecknology doesn't advance, I'm saying when anyone can use a staff that makes you almost as good as any master mage, there isn't much of a point to sling metal rocks at each other. Besides, arrows can be enchanted along with the bows.
The reason there are inventions is because there is a need for something better. Why make a gun that has a hard time hitting anything when you can pick people's heads off with an enchanted bow and arrows? There would need to be a reason for the improvement. Human's came up with guns. Now, what would we have come up with if we could enchant our equipment? That's the route we should take. TES shouldn't follow our time line just because that's all we can go off of, it should follow its own now.