Actually, Wi-Fi is cheaper at delivering Internet access to teacher and lab computers than wired connections. While slower, there is only a need for one PoE port to cover many computers. For schools with older wiring, this is probably a more cost effective methods of providing that access.
It's been true for hotels. Although this at first seems counterintuitive, for awhile, newer hotels, which had been built with Cat 5 to the room, had wired internet but no wireless, while older hotels, who couldn't retrofit wired but *could* put in access points, had wireless but no wired. Now pretty much everyone has wireless. In the near future, you may be able to guess within a few years when a hotel was built by whether or not there's a RJ45 socket in the wall.