I can understand why you and many others (like game DEV) would think so but it is far "easier" than most people realizes. It just takes a particular insight and perspective on the subject:
Many many years ago I was watching a documentary on a man who creates large acrylic castings. His art work was famous because he was the first one to discover a way to cast this medium greater than 6 inches thick without any bubbles trapped in the casting. This amazing breakthrough caught the attention of a submarine manufacture that had been working on this issue (for large dome shaped pilot cabin windows) but had not cracked it (err...no pun intended.).
They hired this artist to teach their engineers and chemists his procedure. The funny thing is this guy did not even have a college degree. He was a hair dresser by profession and did the casting thing as a hobby. He said he spent a year in the library gather all the information he could that focused only on the subject of acrylic’s physical properties and thermal dynamics. From that body of specific information he was able to pinpoint the issue (the cause) and then once he had the exact reason the bubbles formed in the castings he could compensate the cause to over come it. He said something in an interview that has stuck in my head for years: “If you truly know everything there is to know about a problem then finding the answer is easy”.
I have devoted most of my life to studying the physics, psychology and geometry of melee combat. In fact in my own Historical Combat club I (especially as I am a 1% top ranked combatant in this club ) am often embarrassed in conversations about the history of this or that weapon and this or that Italian or German master of sword fighting (and so on) because unlike my most of my peers in the SCA rather than focus on the recorded historical lessons and observations of these great fighters studying the flowery language of sword fighting as an art form, I decided to take a different approach.
One of my other hobbies (started when I was 8) for years was stage magic. In a similar way magic tricks like slight of hand use to be taught as an art form where even the best practitioners did not understand the science of what they were doing. Then some very clever magicians in the 50s decided to change that. The categorized and anolyzed every single magic trick in every book they could find from around the world. To make a long story a little shorter they discovered the science that was hidden in this art form and wrote a book called the Trick Brain. After reading that book in my youth I knew I could do the same thing with the art of swordsmanship. I went on to spend 30 years of my life doing so.
My book on the subject: http://www.spookyfx.com/book/TROMP.HTML
The interesting thing is that a great deal of this heavy weapons science can be directly used in PC games. For years now (about when doom came out) I have been working (on paper) many different versions of “game mechanics” with the idea that someday I might use it in cooperation with programmers to make computer sword and shield combat simulator or at least get close enough that the concepts would work for games.
One of my more basic suggestions that would work for oblivion easily would be this:
Let the PC stats determine the fine small movements needed to complete a difficult parry (angling and moving the weapons or shields small but critical amounts to try to deflect the force of an attack) but allow the player to override this with a rudimentary stop block.
If the player press and holds the block buttons it is a simple block, if the damage is too high (such as from a giant with a battle axe) the shield or weapon takes damage and the force knocks the player around and may even hit them with some damage. If the player taps the block button it is a parry and then the PC skill determines how effective it deflects the damage above and beyond the block (but not instead of a block as it seems it will be in Skyrim.)
And then on top of this you add a chance block ( the chance that the attack hits the sword or shield based only on the size of the weapon or shield compared to the size of the PC).
I have done more than 75% of what I described above already in a POC Oblivion mod I made (as Oblivion already did 50% of this anyway). I had really hoped that because Bethesda had gotten it more that half way right in Oblivion it would be as much as 70% right in Skyrim. Then I might be able to mod Skyrim close to 100% to this simple but realistic version of melee game combat.
Unfortunately Skyrim Melee combat seems to be going in a totally different direction now.
Edit: I really really hope I am wrong about the direction Skyrim melee combat seems to be going, I guess I will know more after the game play movie tomorrow.
If someone has a good heavy war axe swing at you that connects, you may be able to absorb some of it through blocking with a two handed sword, but no way you can parry it with a one handed sword (or even a trapping weapon like a japanese sai). A sai might work against a normal sword, whereas a normal dagger might fail. The rules governing this would be fairly complex and hard to understand. To get it right and balanced - probably a nightmare. A challenge for rebalance modders, sure, but it have to be believable also for the console players.
It's something I want to see, without outcompeting proper blocks and the importance of having a shield, but I can't really see any good ways of implementing it and do control assigns that wouldn't make it overly complex.