Granted, most of the recent TV buzz has been about, rightly, “Mad Men”: Who wouldn’t want to spend summer Sunday nights delving into the deeply misogynistic psychosexual underbelly of a Kennedy-era advertising agency?

But in the big picture, the more interesting effort of the season is an Internet-only offering. “Dr. Horrible’s Sing-Along Blog,” from “Buffy the Vampire Slayer” creator Joss Whedon, is not only hugely entertaining, but it’s another big nudge toward that future where the entertainment screen will be the entertainment screen, and users won’t worry whether it’s called “Internet” or “TV.”

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