I think this is another clear case of difference between what the rules are and what the rules were intended to be for.
It's my understanding that this kickoff out of bounces rules was for
1) Kickoffs that were out of bounds
2) Returners catching the ball with their momentum clearly taking them out of bounds as they were in the process of the catch
The Packers did NOT manipulate the rule ... they simple used the rule in a situation that it was not intended to be used for (and I want to say they manipulated the intent of the rule, but I'm not sure that's quite right, but closer than they manipulated the rule).
The difference between Cobb and Monty was that Cobb's momentum was clearly taking him towards out of bounds... though if memory serves me right... Cobb did have to jump to reach the sidelines, and it wasn't strictly him running so that might of been manipulated the intent as well... but Monty's way clearly wasn't the intent of that rule (IMO).
Also I believe (not completely sure though) a week or two before Cobb's jump out of bounds, Adrian Peterson did the same thing... but he did not jump (like Cobb did) and therefore he got two feet in bounds and therefore it was a catch/return of zero yards where he went out at.
But the Packers have been on the wrong side of these rulings too... I guess teams were banging up long snappers too much, so they put in a rule that you can't line up across from them because they did not want the LS to banged up, so stopping/limiting physical contact with the LS during the snap was the intent.
And of course the Packers decided to get creative and have DT Corey Williams line up across from the LS (on a FG play) at a weird angle (say 50/60 degrees and nail the OG next to the LS so he couldn't get down the field (and he would be in the way of the LS trying to go down field too). Of course flag comes out... because technically the Packers broke the rule about lining up across from the LS. And Madden in the booth went nuts... saying over and over that's wasn't the intent of the rule... the intent was to stop physical contact of the LS during the snap... and I believe the team might of gotten a first down and then the other team got the first down and then I think maybe a TD and the points were the difference in the game (I think... again, that was a while ago... memory might not be perfect on that)