Uh, he explodes after Goku punches the hole in his chest. That's why he didn't regenerate. It was just a delayed reaction.
Not to mention when Piccolo got his energy drained by Cell and had to regenerate a new arm, he had to stall for time to regrow said arm, so it's clearly not instantaneous enough to heal in-between holepunch and explosion.
And if this post came out a bit snarky, it's because I can't help talk about DBZ in an aggressive tone after spending so much time on DBG. >_>
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Will not remove this line of my signature until the Seahawks, Jazz or Rockies win a title (Started 5-16-09)
SuperNiceDog: Guru winner