It is client driven in some cases. I can only really comment on Aberdeen, but the L crews have used the sim for a long time and there wasn't an L2 sim. When the L2 sim was approved CHC chose not to use it but Mobil insisted on it which is why they are in the crazy situation where only some crews are checked on the sim, and they are the only crews mobil use.
I think this is crazy and have never understood how it can be justified. A number of L pilots have refused to go on to the L2 because of this. Even the Mobil "approved" crews go annually compared to biannually on the L.
Sorry this has gone off thread, but it was in answer to soggyboxers' question.