Regarding the punishment, let's face it the Patriots have gotten away with murder and Goodell covered for them. He burned the spygate tapes and he never punished them for using a second audio channel in Brady's helmet to circumvent the cutoff period rule (and Brady knew about that with 100% certainty so don't give me the stuff about him being a quire boy who never participated in the cheating).
This last episode, though minor, was the straw that broke the camel's back. The pats made Goodell look like their chump one time too many. Ironically, Goodell still looks like a chump but that's because he's an incompetent PC fool, not because of the Patriots.
That is a good, succinct summary of the legal issues.
I think part of the reason Goodell went after Brady so dishonestly was because of spygate.
But in this case Brady did not do anything illegal. He would not want someone screwing around with the footballs instead of have them consistent.
The Ideal Gas Law and the two different gauges explains the difference in psi.