Since Netflix never (edit: rarely) releases Blu-Rays for their original content, there's no source to produce high-quality versions of their 4K content right? Could be wrong but I thought webrips that screen capture are relatively low quality because they're reencoding a video that's already being compressed for streaming.

Don't know if I notice these things much personally but if someone already cares about 1080p vs 4K they probably would.