Let's start with a little bit of history.... routed mode was the only mode on the WLAN appliance from the start.
As far as I'd remember bridge@AP was release later in version 4 and bridge@EWC in version 5.
So from the start routed mode was the way to go as there was no other option.
From my personal experience the problem was that a lot of customers didn't unterstand the concept as about every other vendor was just using bridge@controller.
Right now I assume most of the customers use either bridge@EWC or bridge@AP or a mix.
That would mean the customers core router does the routing instead of the WLAN appliance.
That doens't mean that routed mode is a bad thing it's just a design decision that you'd need to make to best fit your network setup.
One thing that it could come handy is if you don't want to forward all the wireless clients MACs into your network.
Let's assume a fully loaded C5210 - I think the max. clients on the controller is 16k.
So in bridge@EWC that would mean that you forward 16k MACs on the controller port to the switch.
In routed mode this 16k MAC are hidden from your LAN switch as the WLAN appliance act as a router between the WLAN cloud and the LAN.
