Probably uses a different interface. Nevermind that most emulators don't worry too much about the parallel ports...
The serial port is standard RS-232. The parallel port was the "Centronics Connector".http://en.wikipedia.org/wiki/IEEE_1284
Centronics parallel is generally compliant with IEEE 1284 compatibility mode. The original Centronics implementation called for the busy lead to toggle with each received line of data (busy by line), whereas IEEE 1284 calls for busy to toggle with each received character (busy by character). Some host systems or print servers may use a strobe signal with a relatively low voltage output or a fast toggle. Any of these issues might cause no or intermittent printing, missing or repeated characters or garbage printing. Some printer models may have a switch or setting to set busy by character; others may require a handshake adapter.