One of the biggest questions in the outing revolves around Sheldon's family not attending his Nobel Prize awarding ceremony. While he didn't forget to thank them during his acceptance speech, it was still odd that Mary, Missy, and George weren't there when Sheldon achieved his life-long dream.
Sheldon states, "speak for yourself. I'm in college on a full ride, but I wish you all luck," before leaving to further drive his point. This offers insight into how Sheldon sees himself in relation to his family, in that it suggests he doesn't think they helped in his professional success because he was essentially sending himself to school. It also hints that he internally separated himself from his family woes to a degree, knowing his intellect provided him a way out. This perception could be the reason why Sheldon didn't push for his family to be there during his Nobel Prize ceremony, and why they didn't push to come - as Sheldon's academic life was made separate from his family life from an early point.
In terms of storytelling, however, it actually made sense that they weren't in the pivotal scene as it was meant to highlight Sheldon's friends as his family, at least in the sitcom.