No not true, the design of the upper and lower intakes can easily allow air to enter one bank more then the other. This is one reason you have O2s to monitor each bank. Also, the fuel injectors can be controlled independently bank to bank. An intake air leak does not always result in an erratic idle. If this was my car I would, clean the injectors via the fuel rail. Replace the upstream O2s if they have more then 30k on them. Check all of my vacuum and air hoses for leaks. If I still get a lean code, replace all upper and lower intake gaskets and injector O-rings.
jeff
