Exactly Neil. Being a writer over the years I've struggled exactly with separating the work from the pleasure and in fact got it so thoroughly mixed up in the past that it pretty much ruined my ability to enjoy reading for fun, but with my re-entry via the ereader route I'm regaining that enjoyment and I'm here to report that it is working and also that I do hope to get back to the writing (work) as well.
The main difference in the two scenarios you indicate is that in one case -- the pleasure reading of the published book is that it should have already gone through the editorial process and should not contain the warts and errors and omissions that could very possibly be in a first submission to an agent or publisher.
I think someone above mentioned Hemingway - "The first draft of anything is shit." and ofttimes the first submission still has the smell.
but a published/finished work should not.