Even if NetFlix only supplies SD, you can still buy or rent BluRay.
It's not just about quality. Pirates want:
1) best quality
2) to keep the product forever (not a rental)
3) prices comparable to a basic no-frills rental service (ie, cost of usenet sub)
4) everything on demand immediately on release + instant delivery
Today, providers can supply some of those depending on which service you're talking about. Do you think you could make a viable business model by checking all of those boxes?
I think its more:
1) DVD quality (no more no less) more = too much HDD Space/download times and less = ...less

2) option to keep forever OR delete (maybe it was a bad movie or it was good but no interest to watch again) no feeling of wasted money by deleting it
3) no unskippable ad's at start, no FBI warnings or other rubbish
4) everything on demand immediately on release + instant delivery
