Blu-ray comes with more extras probably to justify the extra cost involved
Blu Ray disks are 25GB, 5 times the storage of a standard DVD. Plenty of room for the Blu Ray movie, the DVD version, and every conceivable extra including bloopers and out-takes.
Most DVDs were dual-layer, so 9-ish G - not necessarily full, but often taken to a buck-and-a-half, just to make it more awkward for those wanting to make, um, unauthorised "backups" on single layer DVD-Rs. I seem to recall that when that great, long, epic, um, big-word, film Titanic came to DVD, at first (due to it's length) the DVD release wasn't anamorphic - I believe because of the amount of data. Not sure whether it was ever re-released as anamorphic on DVD - but if so, they probably had to cut some corners, sorry, make some optimisations to make it fit.
That said, don't know much about bluray disks, having never done much manipulation, but doesn't much the same apply - single layer 25G, dual-layer 50G?
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