All it comes down to, will it break the team or the future of the team?
Right now the Chargers have a favorable position to spend that much on Rivers. The roster is very young and the free agent signings have already been established. There is money to throw and that team is good to go: the roster is set right now and for the next few years with the money looking right. From here on out, the draft is the most vital for supplying the team's great players. I'm completely confident, especially with the way the division looks that this is a play-off team, right now. Don't have to spend another dime.
If this was a year or two ago, no way they throw that kind of money at Rivers, I wouldn't want them to. But because they got a lot of great pick-ups and have hit on their draft picks and coaching staff, no problem at all. Sucks we'll probably lose Weddle, but older safeties aren't the most efficient ways to spend your money.
I'm not familiar with the Giants, but outside of Odell, are there a lot of holes free agency can fix, any youngsters that will probably demand a pay day? Is there a lot of proven players on the team right now that are guaranteed to be on the roster? That's all it comes down to. If not, then spending all your money on a QB may not be the best investment.