Race time limits?

There is one sprint in my area that officially has a time limit (just total time, not broken down into swim/bike/run) but I think that was done because they had a guy one year who took more than 4 hours to finish.  I happened to be a volunteer that year and didn't get to leave my station - the last water station on the run course - until almost 1 pm.  This was for a race that normally starts at 7 am.  Granted he was probably one of the last to get in the pool, but with only 300 racers he would still have started by about 8.  

I know this is an unusual situation and it's the only sprint that I know of around here that has a time limit, but it wouldn't hurt to check with the RD just in case. 

Cut-Off Time:

All participants must complete the race in under 2 hours - 30 minutes. Race officials reserve the right to pull a participant off the course if it appears as though that participant will not be able to complete the race in under 2 hours - 30 minutes

Most of the SPRINTS in the NCTS (north Carolina) seem to have this time limit.

the Sprint is 750m swim/17.5 mile Bike/5k run

I'm new to tri's, out of shape, and very slow.  I did my first and only (so far) sprint tri in May, and although I finished the whole thing "unofficially", I was for the record a DNF.  On the bike leg, I came in 15 minutes behind the next slowest participant (who did officially finish the race) and was met by a volunteer in transition who told me I could continue but would have to turn in my timing chip at that time.  (I'd emailed the RD prior to the race with no response, and when I asked the question at packet-pickup, I was told "Don't worry about it."  Very frustrating.)  Since then, I've noticed several sprints in the Maryland/Virginia/Delaware area that post cutoff times (some for individual legs and some for total finish time).  But from my experience, I wouldn't assume that having no posted cutoff times necessarily means there are no time limits.