Is your outgoing line truly limited at 100mbit/s or does it allow bursting?
It's not too surprising that applying a bandwidth limit at the AP level will result in sometimes getting lower amounts, especially on TCP based speedtests like Speedtest.net. Ruckus AP's do let a little bit of bursting if you haven't been pushing up against the capped speed, but it seems like it's on the order of milliseconds of bursting.
FWIW, on my 250mbit connection (where my ISP provisions it at a max line speed of 350 or so, and it throttles down gradually to 250), I've tried the speed limits on a T300 from 10mbit up to 50mbit and it's able to accurately track all of those speeds. Running 9.12.2.0.204.