It's interesting to see how tiny Netflix mobile download files are.

200MB - 300MB for full-length movies, ~150MB for series episodes. This is on "Standard quality", but still.

After some quick Googling (grain of salt) I see that a standard DVD of 4.7GB tends go have (usual encoding) up to 135 min of 480p video. That's a big difference! Even when considering that modern encoding might be more efficient. It is lossy compression, and the lossyness seems to be cranked way up.