Weird - Audio books are supposed to be being reduced to 5% from 13% originally according to the handy dandy charg - would have thought the same was true for electronic books which are not explictly listed. This would bring them in line with paper books where previously they would not have been. But you are correct as far as Kobo seems to be applying it - I paid HST on post-July 1 purchases and only GST on pre-purchases. There should be some saber rattling about this for sure. Curious to hear what the kobo rep has to say as they must have looked into this before they made their decision as to what to charge.
http://www.rev.gov.on.ca/en/taxchange/pdf/taxable.pdf