The Pats could have just as easily lost starters to injury, in a game with no playoff implications for them. The fact that they didn't & the Giants did doesn't differentiate the coaching decisions of BB & Coughlin one iota. You can say that they had an extra week of rest, but if Brady broke a leg in that game, there would be just as much scrutiny.
It was a great thing for football to have the starters in that game, playing their hearts out. If nothing else, it was a decision for the purity of the game: you don't earn 16-0 without jumping over that final hurdle, and having that last team push you to the limit. What a great thing for history.
Besides: if the Giants rest their starters, it's a blowout, which definitely kills them going into the playoffs.