To begin, I must say that I don't have an iPad myself. Next, I don't have an answer for the first question, but I would like to add a supplemental question: Do all the iPad readers (how many are there?) suffer from the inconsistencies imposed on the iBooks reader?
In answer to the second question, I think that the iPad's iBooks reader is such a non-conformant beast that we will be forced to have an iBooks edition as well as an epub edition if we want the respective customers to have a favourable experience. This is based entirely on what I have read on Liz Castro's blog
, so it probably should not be considered definitive. The main points are that iBooks allows both audio and video, but in non-standard ways, and that embedded fonts are only possible through very messy workarounds. See her blog and her book for more details.
Those are my thoughts...