Why is this so expensive to buy?

Why is VoD so expensive to buy on DVD? The complete box set costs £49.99 and the single discs of series 1 and 2 are £14.99 and £11.99 each. You can buy the complete box set of One Foot in the Grave for £15.00 and the complete box set of AYBS (12 discs - 69 episodes) for £27.99.

When I decided to buy VoD, the box set was £70 on Amazon. I ended up winning it for £11 on eBay. The prices are ludicrous, especially for a BBC series. The VoD is good, but £50 is taking the piss.

ROCK STARS HAVE KIDNAPPED MY SON