Two more things to add about banks, one is that other people will be depositing money. This means you could rob the shopkeeper while he's on the way to the bank. The other is that the shopkeepers can have some money to buy your stuff in the store, but keep most of his money at the bank. One or two robberies won't put him out of business this way, and if you wanted to sell him an expensive item, he could get the extra money from his bank to buy it from you so you don't have to take a huge loss on it. The bank will be the means for you to be able to sell your high end gear to shopkeepers.
Very good Shades. Your post actually reminded me of a topic I wanted to post on previously, but I'll just mention that here.
Now, I know it's been confirmed that we can affect the economy of a town/city/hold by damaging important economic infrastructure. This got me to thinking....if Beth has decided to put in the option of changing the whole economy for an area as large as a city, could we not change economic status on an individual level? What would be restricting us from ruining a rich noble? Or raising a peasant to a state of wealth? Or perhaps for an advanced level quest, perhaps we could blackmail a shopkeep to get free items and/or a permanent discount? Or destroy the workshop of a rival blacksmith to make him leave town, leveraging out the competition for our personal blacksmith, earning us a huge discount there? The options are endless.....and great for making income without dungeon crawling constantly.
With all these ideas, and the inclusion of mercantile previously, which supposedly is now added to Speechcraft, I'm seeing many more economic-based quests and opputunities for the player than ever before in TES V. Banks could be a huge part of this, as well. I always did think it was disappointing to have a half-hearted attempt at a mercantile skill in Oblivion, only to make it a waste of time instead of the boon to the player that it was supposed to be. I'm sure Skyrim has fixed that and I would expect to be pleasantly surprised all around.