I think that there are really 2 questions which are probably best considered separately:
1. The procedures that helos are required/asked to adopt;
2. the RT phraseology used.
1. It must be everyone's experience who has flown heles in different places that airfields ask heles to do widely differing things. Others have run through some of the options, from treating us just like planks through to a complete free-for-all (i.e. pretty much do what you like).
When I have flown regularly out of or to different fields I have sometimes talked to ATC about why they ask what they ask for. Again the reasons seem to vary. In some cases, heles are rare, so thay do not make special rules, and treat us like planks (because they do not know any better, or there is no particular need to generate special rules). In other cases, usually where there are significant regular hele ops, special rules are made. Hopefully these get promulgated in the various flight guides. Very often, these get agreed with the local hele operators, which hopefully means they are likely to be practical and realistic. However, there will be cases where what is agreed for certain classes of hele are not sensible for others.
I will always remember a departure from an offshore helicopter airport, that I made early in my flying career using an R22 with strong onshore winds. I wanted to go inland, and the clearance was "depart direct". However, my heavy R22 would not have appreciated such a downwind departure. Despite being inexperienced at the time, I summoned up the courage (as a junior low time pilot) to ask if I could depart into wind - no problem at all. ATC thought they were giving me a good clearance because the offshore guys would have been happy with such a departure.
Sometimes, it has to do with the "style of management" of the SATCO or ATC manager of the airfield too.
It probably makes a big difference whether or not there is "control" at the field (as compared with just flight information) and whether there are IFR departures or arrivals, which ATC are there to protect.
I think you would have to have the wisdom of Solomon to generate a set of rules for heles to suit all occasions. If it were done, rest assured that sone rotary pilots would not like them.
2. In respect of this aspect, there must be mileage in standard phraseology. However, like in lots of areas of aviation we are often too rare to bother about or generate special rules for. (Just look at the nonsense situation where we have to do plank ground school to obtain some of our helicopter licences, because the regulators have not generated hele syllabi).