Double click to install xcode4.1, located in /Developer
ios simulators included in xcode4.2 is 4.3. Path:
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
Double click to install xcode4.2, located in /Developer
ios simulators included in xcode4.2 is 5.0. Path:
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
Double click and drag into Applications to install xcode4.3.1
ios simulators included in xcode4.3.1 is 5.1. Path:
/Applications/Xcode4.3.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
Double click and drag into Applications to install xcode4.5
ios simulators included in xcode4.5 is 6.0. Path:
/Applications/Xcode4.5.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
Finally, simply put all versions of simulators to the path where simulators are locate in xcode4.5.
Note: You may need to update the ios simulators in Xcode->Preferences->Downloads so that they function well. The v4.3 simulator may not work in 10.8 OS.