Yes, after reflecting on it, I thought exactly the same thing. It was probably hard for Andrew to face the fact that William seems to have everything going for him - he's starting out in life, with a beautiful bride, a promising career, and personal popularity. These are three things Andrew also had when he was young, but doesn't now. I agree that Andrew has "second son syndrome." Even after William and Harry bumped Andrew down the line of succession, he could still feel like the "second son" in many ways because William and Harry didn't perform public duties. Now, it's like William is being launched into public life and Andrew is slowly fading into the background.
I read in the Daily Mail a few weeks ago that Andrew's trade ambassador role may be quietly changed - he won't be affiliated with UKTI anymore, and won't be sent overseas either but will only promote business in Britain or Europe. I don't know how true this is - but if it is true, you can see how Andrew could be having a mid-life crisis, thinking, "What have I made of my life - is there anywhere I'm really needed?" Even his girls are grown up. Put all these things together, and it's easy to see why Andrew was off in his own thoughts during the wedding.