Morrowind: Start the game with your character being dropped off at a prison island/community.

Oblivion: Start the game with your character in prison.

Skyrim: Start the game with your character being lead to their execution.

...

Bethesda doesn't seem to believe in 'heroes' being a stable, law-abiding citizen do they?

We start out in a prison cell in Arena also. Really the only major Elder Scrolls game that doesn't begin in prison is Daggerfall. I've always seen the prison beginning as a kind of running joke between Bethesda and the fans.

I think another example of Bethesda's running jokes are the rat quests. I'd be surprised if there wasn't a rat quest in Skyrim too.

First Companions quest? I think so.

I thought in Arena we weren't actually in there for breaking the law, but some guy (Jagar Tharn?) shoved us down there.

Who says the CoC and nerevarine broke the law?

Its a running tradition which some people don't like or get.

No one ever said you're in jail because you're unstable or not law-abiding. Perhaps you committed a crime, but perhaps you were framed or something like that. They pick the prison starting area because it immediately gets the player thinking of why their character is in prison, and thus the roleplaying begins.

You're missing my point. In Arena, we know why we're in the prison, and it's not for a crime. In the other games it's left open, but it certainly was never the fact that we were captured by "the bad guy" in any game other than Arena.

I believe it's been stated that it's tradition.

The player being ordered for execution in Skyrim does imply that the character would done something rather extreme, though. Unless the laws have become *really* corrupt in the 200 years that have passed since Oblivion. Which makes sense, since the Empire is at the brink of collapse at this point.