I see most of this thread is necro'd, but FWIW I have the 400ohm version of these. And the reason the foam covers are missing is probably because they've disintegrated, like mine did (I inherited than from my dad).
These aren't a bad phone if you find them second hand, they're very capable as you'd expect form a fugly monitor. I have the DT250 as well, and in comparison, the 100 has more pronounced bottom end and a bit more clarity at the top. The mids lose out a bit, and this is where I think the DT250 does better. i'm running them off a Lehmann clone which has plenty of grunt but not much finesse.
Because of the fit and the pleather, as well as the darker sound, they do sound more like a closed phone than the 250s do.