Play vs. Learning (Maybe)

This morning during our independent reading time I was rereading Reading with Meaning by Debbie Miller (an absolutely fabulous book). At the end of a chapter I came across this quote:

"Once children begin to integrate their learning into their play, the materials are no longer an end unto themselves; they've become another means for creating understanding and constructing meaning. They've become a means for living the learning."

I sat there, staring off into space for several minutes. (I would chastise my students if they were staring off into space for several minutes during independent reading. I will have to be more careful about that.)

My initial reaction to this quote was a firm support for it. However, as I mulled it over I began to question my response. Is it a bad thing for the materials to no longer be an end unto themselves? Does everything have to come back to the learning?

I can't decide if I'm looking for a happy medium between what Debbie Miller is describing and a completely free play time or if I think one or the other is better. I'd love to hear thoughts.