I'm not saying that a BD rip is the same quality as a DVD rip, in most cases it will not be depending on the sizes of the files. There are too many variables in this to explain it in a simple manner though. What I am trying to say is that a DVD rip of 1GB or a BD rip of 4GB are not of the same quality as the original DVD and BD respectively, and that most probably the BD rip of 4GB doesn't really offer that much difference to an upscaled DVD, or at best will offer DVD quality just at a higher resolution. This is down to the codecs, and yes, the MPEG4 based ones are much better than MPEG2 based ones at getting size down while retaining the quality. Any sort of compression is bad IMO, but it's something that is necessary, because disc sizes and data transfer rates do not exist to have the raw file.
That 2TB figure I came up with for The Dark Knight was based on a 1080p image (1080i would be the same because movies are recorded still in the main at 24 frames per second), and it comes from these assumptions.
1 frame 24 times per second.
1 frame is 1920x1080 pixels by 32 bits per pixel (4 bytes).
That gives us for video data only (no audio) 32x1920x1080x24 or the staggering sum of 1,592,524,800 bits per second or 190MB per second. That's 11.4GB per minute, over a 2 and a half hour movie is 1.7TB for video alone.
The day will come when we don't need to do compression, but we are nowhere near it at the moment, but the major point is that you can compress to a certain level without the human eye/ear noticing any difference at all, which is a good thing in that we can use resources more effectively. My original point simply was that a good quality BD that is ripped to 4GB cannot offer the same quality, but many people will not really notice the difference, especially when cost come into the equation, because at the end of the day there is a ratio between cost and quality that provides the perceived value to the consumer, and it is this that can possibly effect the objectiveness of the said consumer. On a technical level it is different.