ACFT was dispatched with inop airframe deice sys, tho an opnl deice sys was rqrd for flt in known ICG conds. Drg dscnt to lnd, ACFT enctrd lgt ICG conds. Capt believed ACFT could 'handle it' & contd dscnt. As he bgn ILS final apch, he noted sgfnt incr of ice accumulation & used higher than nml apch spd. As full (50 deg) flaps were set, ACFT bgn buffet & pitched nose dwn. Capt corrected with full back pres on ctl column, but ACFT lndd hard, gear collapsed & ACFT slid abt 3600' to a stop. No preimpact mech anomaly was fnd, except for inop deice sys. Inv revealed plts had rcvd printout of wx fm co computer sys with sfc obs & trml fcst, but no area fcst (FA). Plts & gnd psnl were not aware that FA was avail at co wx trml. FA fcstd lgt & ocnl mod rime & mxd ICG in clds & precip abv frzg lvl. Wx dtrtd, but plts did not req inflt wx info or pireps. Flt mnl noted tailplane ice may cause nose dwn trim chg with flap extn. There was evidence of tail plane stall, lack of co trng in cold wx opns, deficiencies in use of deicing sys, & lack of FAA surveillance.