If I remember what I've seen and read regarding airliners brought down by bombs, the key technical difference when that happens has to do with metallurgy - IIRC a specific kind of "pitting" in the metal combined with the pressure vessel failing from the inside out. They've had people on the ground for long enough now that evidence of that nature is likely to have been found - enough to cause suspicion, if not certainty.
As far as the recorders go, I'm pretty sure that as long as the recording medium (the little grey cylinder bolted securely to the recorders) appears to be intact, there shouldn't be any issue with reading them...