With modern codecs you're unlikely to notice much difference between a 20GB download and a rip you did yourself.
Mind, it's not worth it for most movies. However, those flames are a good example of why bandwidth can matter.
Which doesn't really matter though, you can also find 40GB files of most movies, they should (if encoded well) definitely match the quality.
The disc capacity contributes a lot to disc authors tweaking codec settings to value quality above file size. Visible artifacts are fairly rare even on complex scenes. You could practically believe you're watching a lossless source.
It's just that I come from VCD rips and still think that anything better than DVD is fantasticly detailed. Just never had the urge to let myself get used to better, but I'm starting to with 1080p.