I tend to think of it more as a tradition in TES, but that doesn't mean traditions can't be broken.
IIRC someone said pre release, that the whole "begin as a prisoner" thing was that it made it a whole lot easier on the player to create his/her own back story...a clean slate if you will. Starting as a prisoner does that job pretty good.
Yeah it's a tradition, but I'm sort of of the belief that traditions in such a series are a bad idea.
Fallout series? Vault Dweller had a dog as his constant companion, Lone Wanderer had a dog as his constant companion, and the Courier? The Courier had a....friggin' floating eyeboat thing. Even something as small as that I found so refreshing, cause it broke the mold, made the Courier unique and gave him more character. The Courier also broke the molds of being a good karma protagonist (feels more neutral karma since you HAVE to gain bad karma at some point; someone will ALWAYS view you as evil), using energy weapons (guns are better) and wearing power armor (not as useful for him as it is for others and the game seems to suggest going against the BoS this time) and again, it only made New Vegas feel
that much more unique.
If they did a game where you didn't start out as a prisoner and chose an unorthodox setting again (Cyrodiil and Skyrim honestly don't feel "unique" but rather more like the "defaults" of Tamriel, a place like Black Marsh, Elsweyr or Summerset Isles would feel unique) with mechanics that seemed to lean towards a thief or mage playthrough then I definitely wouldn't complain.