Your actually wromg my friend. No game is ever made perfect and there is always little tweaks/bug fixes here and there that can make a game better.
Konami are very clever in the way they release their WE/PES series. Let me explaine.
WE is released usually around the August time of year, as we all know WE is only released for the Japanese market. Doing this makes it easier as they don't need to make localization versions which can take a long time (submitting the code to Sony UK/US, Microsoft UK/US etc usually takes about 2-3 weeks, if it fails it will have to go back again for another 2-3 weeks after the problem has been rectified).
So in turn they can get this product out to the Japanese public a lot quicker, which also helps for market reaserch and feedback whilst PES is still in its product life cycle.
All the defect/bugs and genral gameplay issues that have occured on WE will then be fixed in the PES version, therefore making the game slightly different and slightly better.
It may seem to be exactly the same, but infact it is not.