Wireless LAN uses a contient method to send/receive information (similar to CSMA/CD of classic ethernet)
if you have a lot of clients, this can degrad the performance of communications....
Actually don't exist mechanism similar to switchig in wireless ethernet. You only can separate traffic in different channels (this depends in configuration of access points)
leased lines are used to inter-communicate networks and the rate (no performance of traffic!) is always similar due to communication is betwewn two routers that send packets to the other