Let me start by admitting that I'm doubtful a distinction between art and entertainment is anything other than arbitrary. But a question came to me while lying in bed unable to sleep.
Does "art for art"s sake" turn art into entertainment? More specifically, if literature exists for no sake other than itself, and if literature can teach us about nothing but itself, then how does it differ from other forms of entertainment (say, a derivative sitcom, or a board game)? It is a different pleasure, but is it a fundamentally different type of pleasure?
Certainly there is a difference in the act of creation, but I'm considering this question as a reader, not a writer. When I choose what to do with my time, if I read a book rather than watch a derivative sitcom, or play a board game, how is the reading different than those other activities?
I certainly think something different occurs when I choose to read a work of literature over other forms of entertainment. But then, I have some quirky (perhaps mystical) beliefs about literature's purposes and possibilities.
One might go further to seek the differences between reading a novel instead of other types of (non-fiction) writing (what is fundamentally different between reading, say, Philip Roth's Portnoy's Complaint or Erik Erikson's Young Man Luther?). I'd ask that not to say there is no difference, but to know what those differences are (and to seek what similarities in the reading experience there may be).
But these may be stupid questions, mere garbage caused by the late hour.