That's too simplistic for me Aus. I'd agree that preparation for every 'away' environment starts with:'it's hard to win in an opponent's stadium, period. It comes down to execution'. With that said, some away games will see bigger advantages for the home team than others/some away games will have more room for error than others.
Based on record but also on historical HFA level I would say winning in Green Bay definitely provides less room for error which definitely requires a higher percentage degree of successful execution to achieve victory.
Personally I'm reveling in it with the Patriots playing in GB this Sunday. The Patriots have swept aside division leaders Denver, Indy, Cincy in the AFC. They swept aside division co-leader Detroit in the NFC. Now is the piece de resistance of the NFC, playing arguably the best team in the NFC (GB is #2 in point differential, 22 behind #1 Patriots) in arguably the hardest place to win at in the NFC. If the Patriots go into Lambeau and win by a straight up double digits it will leave little doubt in my mind Patriots are playing a level of football that, basically, the rest of the league isn't playing (then let's hope it stays that way!).