PWM, some other that GM uses, EOBD, and CANBUS. And all european cars after 2000 for petrol, and 2003 for diesel are required to have EOBD suppost (as do most japanese cars) or CAN BUS after 2008. This is mandatory by the european laws that limit car pollution and emissions.
Perhaps you used a defective ELM327, or an ELM323 on your VAG?
Like I said before, the VAG-COM is a proprietary interface for a proprietary software. They only couple up with each other. If you want to use ELM compatible software, you must have an ELM interface.