For one reason or the other which I didn’t bother taking the time to research some some applications get duplicated within OS X’s Open With menu. Doing some searching around online I found the following command that helps resolve this issue. Just open up the terminal and type in (or copy paste this):
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user
Once this is finished just restart Finder with Control + Option + Click on Finder Icon in the dock and you’re good to go. This has been tested and works in Mountain Lion and should work in previous versions as well.