NASA's final shuttle flight slips to November

Why is there such a "Mind Set" for some of the powers that be, that their must be an END to the ISS! One of the reasons for the current design was to be able to replace segments and continue adding on segments as needed. There should not be an Expiration date! I have read many opinions from NASA people saying it's worthless, in the Wrong Orbit, underpowered, and can not move far on it's own. Well then FIX IT! And if the Shuttle is to Old, Build a New One. We certainly have missions of importance for it to do.