@Robin,
Not all networks connect to external resources and with Ruckus Unleashed not requiring a separate controller or internet connection it is theoretically possible to have a wireless-only network. E.g. if all the devices on the network were wireless and no internet or hard-wired connectivity is required, then the network, in theory, could be purely wireless.
However this is rarely the case and as you say; where the network is for internet access, a 'Root' AP is usually connected to a switch or router and all data traffic will pass through this point.
On your second point you are absolutely correct; a wireless mesh is just as much (if not more) susceptible to the same issues that can affect AP to Client connectivity. Furthermore for each Mesh 'hop' the available bandwidth is halved and latency increased. E.g. if starting off with 300Mbps (data rate) with 4 hops, bandwidth available at the end of the 4 hops will be equivalent to an 18Mbps data rate (UDP throughput of less than 9Mbps), even in perfect RF conditions.
I hope that helps,
Darrel.