That's because most PDAs implement the IrDA standard which is designed for short range and device-to-device communication - to control a TV you need Consumer IR. Implementing IrDA would be a waste of time/space/money on the RX-51, it's been pretty much rendered obsolete these days by radio based technologies, but Consumer IR could be an interesting addition and would give the RX-51 something the opposition lacks, although I doubt it would ever replace my Harmony One.