I have completed several government retail scale interface certifications. Any weighing scale that is certified for commercial use has to show the data cannot easily be tampered with. For this reason it would not be possible to certify a scale with a network or wireless connection. Hence they are all serial interfaces, usually RS-232 or RS-485. In theory a USB or Parallel interface would achieve the same level of trust, but as the demand is so low, i doubt a scale manufacturer would bother certifying them.