The issue is that some dvds have like 5 or 6 episodes fit in there, whereas others have just 1 or 2 eps (happens a lot with R2s of OVAs, and I bet you know that very welldokool wrote:I'm not sure if I agree with the "these 4 episodes of an anime" instead of picking a DVD thing... part of picking a DVD means you're married to whatever's on the DVD for better or worse, and that in and of itself is a challenge. You never know what sort of neat stuff shows up in those throwaway filler episodes that people abandon for the action in the next ep...
OTOH, having a fixed number of episodes puts everybody on the same level.





