Understand that this guy is being presented as a hero by the media. The public has taken an enormous interest in him and his life. It won't be long before we know his waist size, shoe size and favorite beer too.
You're right that nothing in his personal life should be relevant, but when it comes to fans (the media can be construed as a fantatic providing a broader glimpse into ones life), they will go to any length to learn about the most trival detail about the individual. The personal stuff is especially juicy. The adoration being displayed is almost romantic. People are already selling trucker hats that say "SULLY IS MY COPILOT" and other variations alluding to the fortuitous events of the flight.
Unfortnately, once you've been splashed all over the media, people are going to want to know everything about you inside and out.
Perhaps the media would not have released his grades had they been really bad, nahhhh... Im guessing they still would. The media stops at nothing to air their story and be the first to do so too.