Blu-ray can fit an entire season of a normal SD TV show on one disk - most seasons are around 5 DVD's each - with AVC and VC-1 encoding used it would fit a normal season on a single layer 25Gb Blu-ray - and be far cheaper to manufacture package and buy than a multidisk DVD set.
Of course with more shows moving to 720p and 1080P it would be back to 2-3 Disks per season again perhaps.>>>>>
Planet earth the 1080P series fitted in 125Gb so 2.5 blu rays would have been enough (it comes on 5 x 25Gb single layers disks) - However If they continue to develop better encoders OR AND the 4 layer 100Gb disk it may well be possible to get an entire season of a 1080p series on 1 disk.
Hitachi claim the 4 layer 100Gb disk will work with current players via a firmware update though then again it could be BS.