I think part of the point of this lecture is to enlighten in opposition to Fred Hoyle's steady state theory which was popularised through much of the 20th century. Don't forget that the Big Bang was a pejoretive term coined to discredit other theories. Krauss neatly sums up current observations which are in support of the accelerating expansion of the universe. MOST people are not aware of the current understanding of the observed nature of the universe in which we live. It amazed me how many people, having watched the recent BBC series by Brian Cox, were astounded by what they were being told (depressing as some of it can sound). Much of this has been known for decades. We need more of this type of 'This is what we currently know' for everyone to hear. A bit like software patches and service packs for people's brains :)