⌘T does not open a new tab
I noticed mine didn't either under Mavericks 10.9.5.  

Open System Preferences -> Keyboard - Shortcuts tab, Select App shortcuts

Click the + button and under Application: select Finder.app,
under Menu Title enter New Tab and under Keyboard Shortcut enter ⌘T.

After that in an open Finder window ⌘T opens a new tab.