Amber's story channels the classic head versus heart debate. Many people of a romantic notion always root for heart. In reality, head must sometimes be given the preference. Not all the time, mind you, but in certain situations. The one presented in "My Brother's Wedding" for Amber just feels like one of those times. So while Amber and Bob not being together might be sad, it's the right thing for the character and the show.
Lastly, it is worth noting who Crosby's best man is. The character is named Billy, and he is played by Derek Phillips. Phillips played the character of Billy on Jason Katim's other series, Friday Night Lights. This Billy has a different last name, but fans of Katim, who created Parenthood, will not miss the reference, as Parenthood's Billy acts very much like early Friday Night Lights Billy. Also, this could just be coincidence, but the woman in the green dress that Billy dances with at the wedding in "My Brother's Wedding" looks an awful lot like Dana Wheeler-Nicholson, who played Billy's mother-in-law on FNL.
In all, Parenthood delivers a moving, fantastic season finale. If the world is just, the story will continue next fall on NBC.