Compressing certainly does the trick, Ruffrob. What you've just advocated is in a nutshell what DVD2One and its kind actually do.
However, the question [from Robbyrob] was '100% duplicate in sound and quality', and I was remarking somewhat pedantically that splitting was the only way to retain the original quality. Programs such as DVDXCopy don't do any compressing; the two discs you finish up with contain identical - bit for bit - copies of the original.
I believe that this rigmarole is unnecessary for the majority of people and movies and that there are sufficient reserves of quality in the originals to stand a certain degree of compression without perceptible loss. Other people would doubtless disagree.
The unfortunate fact, as Robbyrob has now discovered, is that unlike CDs, commercial DVDs and writeable blanks are not the same size. And size matters - as the actress told the bishop!