Not true. It happens. A lot! Not necessarily where you are but if you travel round a bit, what you see and hear can be enlightening!
I would say it's terrifying... Could you give any examples when ATC uses relative altitudes? I'm suprised, because using relative alt, ATCO don't know current a/c altitude (that may be reason for using relative alt), neither at what alt a/c will level off. One of primary ATC functions is to constantly know a/c positions and intentions...
Creating local, colloquial "phraseologies" may be funny at time, but there's deeper concern. Pilot's may get used to them and cause an incident on the other side of the Earth, when ATC is using proper phrases. The good example is omitting "2" in altimeter values in the USA - "altimeter 992" instead of "2992". It already caused some incidents in Europe: eg. "QNH 992" is said to pilot and he sets 2992 inches...