This is also a pet peeve of mine and there's a reason for it.
Its because there's 20% VAT (sales tax) on ebooks. This is EU regulation, but can be reduced or removed at discretion of individual governments. There's a petition on HM Goverment ePetition web site. Please consider signing it. The link will take you straight to the correct petition and its open until August -
http://epetitions.direct.gov.uk/petitions/114