I am guessing it's cost but it's interesting to see both TV3 and TVNZ have a mish mash of HD programming of the US shows they air when clearly they all originate in HD.
I suspect it could be cost, or perhaps the provider has elected not to provide a HDi 50Hz version of their programming?
I didn't do a lot of data collection but examples include
TVNZ - Once Upon a Time - 16:9 but SD, American Idol ditto (but could be because they don't want to send the HD version over the satellite), Desperate Housewives(!) - SD and that is a surprise given presumably how popular the show is and the vibrant colour palette it's shot in
TV3 - House 16:9 SD, could be others.