Correct me if I"m wrong, but isn't there usually a bye week before the USC game in the years it's @ home? I think it has more to do with the time of year than the team they're playing.
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They try to time the bye with the ND Academic Calendar's Mid-term break so the athletes can focus on mid-terms and the students are on campus for the games. '11's Mid-term Break is October 15-23. It frequently falls near the Southern Cal game.
SC opted for the mid October weekend back around 1960 after they had lost 4 in a row to Brennan and Kuharich. They (I believe John McKay SC's new HC in '60) complained the weather was too cold in South Bend in late November and that gave ND an unfair advantage. Southern Cal was 3-13 against ND in late November in South Bend (or Chicago). For most of the preceding 3 decades the Southern Cal game was final game of the ND season. In '61 the first year playing in October in South Bend the weather was frigid.
Since the "unfair weather advantage" was neutralized by playing in South Bend in balmy October Southern Cal has gone 10-13-1 in South Bend. That includes the vacated game in '05 that should have been a forfeit and reflects the Trojans current 4 game win streak in South Bend.
Three times in the series, '47-'48, '50-'51, and '55-'56, ND played 2 years in a row in LA. They've never played 2 years in a row in the Midwest.
If you look back through the series the only dominant years for SC regardless of when or where the game were played were under John McKay, John Robinson's first term, and Peter Carroll. None of them had to play ND in late November in South Bend.