An answer from a Republican Energy & Commerce staffer:

It’s true — He came in after the statements. I don’t know the particular reasons. But for this hearing, only the Chairman and ranking member of the full Energy and Commerce and Science committees, as well as the Chairman and ranking member for the two energy subcommittess for E&C and Science gave opening statements. Mr. Barton and Mr. Hastert waived their opening statements, as did Mr. Boucher (and maybe Mr. Lampson) on the D side, so that they could have additional time for questions.