I'd agree that dual weilding should NOT be easy. It is possible to effectively utilize two weapons and there are situations where you'd want to (situations where volume of firepower outweighs the need for accuracy, or where ammunition on demand is needed -witness how dual-weilding was the order of the day in the age of the single-shot pistol -because it was the only way to get two shots off in rapid succession- and steadily declined as the available ammunition in a hand weapon increased.) But ordinarily you do not want to go traipsing about with a gun in each hand.
There should be a large penalty to accuracy, reducable with a perk, and, of course, able to be overcome with sufficient application of skill points -for example today's "trick shooters" who do all kinds of crazy stuff with pistols that's impossible even for skilled marksmen.
Strength should come into play when dual-weilding anything larger than medium-size pistols, and this factor should be doubled for anything fired in automatic mode, and tripled for sawn-off shotguns or similar weapons. (I know a fellow who has a pistol that fires a full-size rifle bullet, very much like the .223 pistol in Fallout -so much so I think it actually IS a .223 pistol- that in theory a very strong man could one-hand.)
The biggest argument in my book in favor of dual weilding, though, is that you can do it in real life. Weather or not you'd WANT to is another matter, but you can do it. I've read about some of the changes from 2nd Ed AD&D to 3rd ed Dungeons and Dragons -one of the things they wanted to address was why it says in the rules that Wizards can't wear armor. Someone asked "what happens if my wizard puts on armor? Does he explode?" So they wrote rules for it instead of disallowing it. The rules basically make it so that wizards don't wear armor still, (-4 to all moving actions since nonproficient, so on and so forth) but since in a tabletop game it's not as easy to say why the player can't do something, especially something as simple as put on armor. Because it's a computer game you can just set a flag that something can't be done, but the computer game should be trying to give the tabletop experience, which is trying to provide a fun simulation of life.
Just like in D&D you can build a character that is essentially a Wizard in armor, I don't see why you shouldn't be able to build a character who can wield two pistols. Make it realistic if that's your problem with it, but it is possible to learn how to use two pistols at once in the real world, so why not in Fallout's world? Do I explode when I pick up a second pistol?