There was a pilot run several years ago to see if it was worth it to discard the 'as advertised' signs. Apparently it wasn't worth it as the signs do actually entice shoppers to buy the merchandise that isn't on sale.
IMO if you're complaining about these signs, you have not been with Target very long. Spot has come a VERY long way in terms of ease in putting up the ad. Nowadays, it's quite simple to get up the ad in a minimal amount of time. Are there still issues? Sure, but it's certainly not as bad as it used to be.