In the ever changing world of WiFi devices, some equipment becomes legacy very quickly. There are a great many still useful devices out there that only support WEP. WPA or WPA2 are beyond thier capabilities. So what do you do? Many companies are setting up blended environments with multiple AP's and networks, each supporting a different encryption method. This way each client can use the highest encryption available. This is kind of dumb however since if part of you network is running WEP, that's the weakest link and running WPA2 is pointless.
Via [techworld.com]