For me, this is all contrived GW customer manipulation. The paperback Glottkin book must have been in print when the hardback went up for pre-order on the GW website (the manager at my local GW store already knew about the paperback before the hardback was released - the company line being that they had underestimated demand and were doing a PB run for the sake of the hobby). The paperback was still in stock on the UK website last time I looked and £10 cheaper than the hardback edition was a month a go. Don't believe any bilge about underestimating the demand from the market - if PB's were already in the pipeline (and seemingly in greater numbers than the HB's) then the HB edition is essentially yet another limited edition option.
If GW are hoping that they can recreate the halcyon days of customers queuing around the block outside the nearest store from 6am in order to get the last couple of copies of a very limited print run then I think they've failed. As others have said, those lucky enough to have the fastest broadband connections can snap up multiple copies and then stick their spares on Ebay at 2 or 3 times the price. Independent web-stores have stopped bothering to list the Endtimes books as they can't guarantee stock. Surely this is going to hurt sales of the new model kits?
If you (like myself) didn't manage to pre-order Warhammer: Khaine then I'd hold fire on paying some opportunist 3 times the price on ebay - I'm sure the PB edition is already sitting in the warehouse. If you really need to know the revelations before the spoilers start to get leaked all over the web then there's always the i-book option ...!?