There are a number of occasions when ATC'ers etc may limit a service. Usually due to radar clutter, high traffic density, limits of radar cover, radar overhead, using SSR only and yes, you are right it is a disclaimer. There was a report I saw by the RAF ATCEB some time a go, stating that ithe use of the term "limited" was getting a bit excessive. I blame the instructors myself!
You will still get info as normal, but, should god forbid, the controller miss something, he/she can always say "ah but you were on a limited service". It is a cop-out in my opinion and used far too much.
On the subject of TCAS, you will generally not be told about traffic that is more than 3000' above or below as it is not a factor, you may however, still see it on TCAS. Also do not forget that TCAS is not very accurate in azimuth and the controller may assess that your relative courses are such that you will never conflict with the aircraft and so, not bother calling it.
This will probably all change when ATSOCAS is all shaken up and we re-invent the wheel!