System Admin is IT related. If you look in your 750B there should be a place where the form describes what SysAdmins do. I assume it mentions something like "administers computer systems, blahblabla...".
BTW, it could be true that RIR-s get send to Dallas, also, I don't think there can be a clear discrimination on ocuupation bases (also, CO might have a subjective opinion to which job markets suffer), but for non-RIR cases this might not necessarily be the case. There was a thread for Colorado SESA (try to find it by keyword CIBER) where number of people with IT related dot codes got approved by Denver DOL (since their cases were processed as Limited Review).
Overall, I think whether it goes to Dallas or Denver depends on how "troublsome" the case seems to be. See, Denver DOL does not have a CO, therefore they can't deal with "troublesome" cases, hence they have to go somewhere else. If the case is straightforward (say, a vietnamese cook's position, with no AD responses over 2 weeks) Denver DOL approves it with a Colorado (or other state) SESA-s suggestion. It seems to me that cases that end up in Dallas have a high probability to get NOF-ed. I'd suggest any interested party to consider plan B, whenever case is sent to Dallas.
Now, the issue of why they get sent to Dallas DOL (obviouselly the slowest of all) and not to, say, Chicago DOL, is of enormous philosophical magnitude. I suppose DOL just happens to have the most exotic tastes in pervertic ordeals.
