It's a brand new engine there might be a different feel
Yes if it was oblivions system copy paste no block for double damage would fail because block is pretty necessary in oblivion and infact thew pattern is block strike or block strike strike but in that game block causes a lot of stagger and is easy to do by holding the button and you easily put the block away by attacking without even bothering to release the button. I removal of block from oblivion would allow you to get staggered and hit and for the most part be kind of useless.
However, that is oblivion. Skyrim is an entirely new engine so I can't say how the flow of combat will be changed. If block requires timing and leaves you open before and after and attacking also leaves you open a fast two handed could be using openings for his combat style instead of relying on blocks. It could go any number of ways.
I'll admit though it seems strange to have a two weapon style with low defense though since with two weapons you can parry with one and attack with the other. That's in reality what differs a guy with a big sword and a dagger like weapon from a guy with a bastard sword or a katana alone. In reality the two handed guy blocks easier while in skyrim the opposite is true which feels a bit weird.
Also we don't KNOW blocking with two weapon would be over powered so people are silly for saying it. Released information so far doesn't give any data at all that points to dual wielding doing more damage then 1 hand + shield. There isn't anything released on perks for two handed. There is released information that you only attack with one weapon at a time. With bethesda's record for balancing in arena, daggerfall, morrowwind, and oblivion it's completely possible that dual wielding will look cool but be stupid and useless to do. I'm hoping thats not the case but the posts saying it will be over powered are just as much speculation as the posts saying it is needed.
So balance wise it depends on how the flow of combat works and how good dual wielding is if it works. Immersion wise having more defense with 2h vs dual wield is a bit silly.