The NTSB has said the same thing about the switch...however, I don't seem to understand how an early stall warning could have caused this accident. Regardless if the stall warning fired on-time or early...the recovery was jacked up, After watching the animation it seems to me that if the stall warning did go off early, it gave the Captain a "head-start" on the failed recovery.
There's several different ways to look at it.
You can say that this accident was caused by hiring a weak pilot and allowing him to continue flying when his deficiencies were noted.
OR
If you acknowledge that weak pilots exist,
the fact that he was slowing to a target speed that was below the stick shaker speed is certainly a causal factor. (along with fatigue, poor stall recovery training, misleading tailplane stall info for the Q400, poor training on the icing speed switch....etc)
I wasn't able to watch all of the hearing, but what I did see led me to understand that they didn't "let their speed get slow" they were intentionally slowing to a ref speed that they (through fatigue or incompetence or both) did not know would set off the shaker.
The aircraft was not actually stalling or approaching a stall when the shaker went off. (unless you know for certain that the capt would not have added power when target speed was reached and the fo wouldn't have said anything if he didn't)
The shaker went off at an unanticipated speed and he freaked out, pulled 1.4 g's and pulled the plane in to an accelerated stall. The FO then freaked out and retracted the flaps (perhaps a pre-briefed item by the captain who had recently seen the tailplane icing video?) and the rest is sad history.
The solution? Don't hire or continue to employ weak pilots. Don't pass the "gouge" around. Skilled pilots don't really need it and it just allows the weak ones to perform mediocre enough to train to proficiency and continue flying.
The over-supply of pilots is one of the main reasons the entire airline piloting profession is in the state its in right now. Even more so at the regional airlines.