compared to a serial port, USB is incredibly complex. the hardware and software required to implement it on either end (computer or device) is orders of magnitude more complex than regular serial; that's why companies sell USB developer's kits and such, with chips and pre-made software that handle most of the dirty work.
the only way you are going to get simple TX and RX lines with USB is to use a USB to serial converter, at which point you are literally just using a COM port anyway.
you could get one of those USB dev kits that has a handful of digital outputs, and use that for some sort of communication, but you would still have to deal with software on the computer side and it would probably be far more work than it was worth.