This decision by SK's publishers reminds me for some reason of the U2 single,
The Fly, on release in the UK for a very short term only (3 weeks I think), so it shot to number one in its first week of release. Had this single been on release for longer, perhaps there wouldn't have been such a rush to purchase and no number one spot.
Here we have a straight-to-paperback novel by SK which will not be available as an ebook until some undefined date in the future.
So, I guess that the thinking is that ebook readers will rush to buy the paperback. Hardback readers will also rush to buy the paperback. The straight-to-paperback format will then be hailed as a success.
Personally, although I was once an avid fan of SK, as I read more, I began to criticise more and some novels I found rather lacking in novelty (Cell springs to mind, but there are a couple of others). I am still always interested in checking out a new SK novel, but I think I'll wait, either for the eventual ebook, or availability at the local library.