I have figured out the reason behind why Sehwag has succeeded more in the longer version of the game than the shorter one .
First of all, I must explain that I am very similar to Sehwag in terms of batting; opener, limited feet movement, doesn't like to get tied down by bowlers, goes for his shots, agressive, etc etc.
Now today I had sat down, and since I had nothing else better to do, I began analyzing my last summer's batting. And I came to the conclusion that I, eventhough am an agressive batsmen, like to play the longer version of the game and not want to get tied down with a limited number of overs.
In other words, eventhough I love smacking the ball and going for my shots, I don't want any restrictions on me (in this case the number of balls I have to make my runs). I don't like to have pressure put on me, instead I would like an unlimited number of overs so that I can slow down whenever I want, I don't have to be agressive at all times. In conclusion, I can be as agressive or as defensive as I want without having to worry about the overs. To actually be defensive in my approach is another matter. When there is a certain number of overs in which I have to make my runs, I fall under pressure and tend to go for every ball and end up losing my wicket. And I think the same applies to Sehwag.
This is just a theory, however, not necessarily true.