The following is from the JISC website (and the survey is not available on the ISBN International web site - not even a link).
In order for libraries to be able to identify and purchase e-books in various formats and from various vendors we need to establish an effective approach to identification of e-books. This is also essential in terms of cataloguing and ensuring that the print record is not replaced by the electronic record. But the question is to what level of granularity do we go to meet demand and what can publishers and aggregators realistically supply? The International ISBN Agency is trying to establish requirements and the simple 4-question survey is designed to assess both the real needs of users and the ability of publishers to satisfy them. Please do take part in the survey as this is an important issue that requires resolution. You can read about the background and the issues associated with ISBNs for e-books in Brian Green’s briefing paper. It is well worth a read.