The zip ties are a quick, easy, and cheap method by which a gun can be "locked" after having been verified as empty. I don't know if it's required by law around here (doubt it) or by insurance companies (more likely).
Every time I've wanted to see a zip tied gun from a dealer's table, they've had more ties there to "re-lock" the thing when I finished. I don't find the zip ties to be particularly onerous. Now, some of the sellers... that's a different story and different thread.