I do not fly over there but RPT into controlled airspace in my experience often a combination of regulations and company SOP's. The 150nm call on area I assume is probably consistent with these guys getting ready for descent from controlled airspace and as such traffic is advised where known, I doubt this would be a CTAF call.
It is then often a request from ATC for the aircraft to call leaving CTA (say FL180) or around 80nm. I know we do an all stations on area (traffic XYZ and ABC Centre) and kill two birds with one stone, ATC may then say no traffic, same traffic as before or new traffic to be expected. We also start listening closely on CTAF.
At around 30nm or around 10,000' a call on CTAF is made which is usually the first call on CTAF with the usual blurb.
We do the usual calls thereafter but I raely hear the 1nm call made.