I didn't get one either. I assume they didn't make one as a cost cutting measure. You know for 100,000 copies they make without an insert, they save a penny or so. :)
Since Whedon writes comics, I could see it resurfacing in that medium. Although his comments about having a feeling of closure with Firefly/Serenity makes me wonder if he might be reluctant to even do that.
I like Buffy but thought Firefly was vastly overrated. It was good but nowhere near what I was thinking it would be. That being said, I'm probably the only person in the world who finds it overrated so what do I know? :) My feelings aside, it's a pretty safe bet though that if you liked...