Someone more cynical than me might think that Apple agreeing to carry the new Band Aid single for its standard 79p price, but donating an additional 70p for each sale they make, is something of a marketing gimmick.
It’s worth noting that the official site sells it for £1.99 rather than the £1.49 Band Aid receives from Apple. And I’m sure that some tracks cost more than 79p on iTunes – couldn’t be bothered to verify this however.