But I do think that if we sit here and state anything but the crew caused this accident we'd be doing a disservice to aviation safety.
Well, it's mostly some human and very often the crew that committs the final error, but that shouldn't prevent us from trying to find out whether that error was induced by some other deficiency.
I have flown the Dash 8 from -100 to -400 for 9 years and I would not dare say that it requires extreme stupidity to move the PLs behind flight idle. The Dash 7 had a weight-on-wheels operated mechanism that prevented this and most jets have some kind of safety system preventing operation of reversers in flight.
AFAIK the F50 got some kind of retrofit gate to lock out beta in flight as well.
Someone mentioned using the props to slow but that wouldn't really work unless the power levers are retarded as well, AND advancing the props makes one helluva noise which one would not inflict on the pax unless absolutely required.