The reason he did this is because one of the singers from Oasis made a big stink earlier this year when he found out Jay-Z was performing at the festival that clip is from. He declared "HIP HOP SHOULD NOT BE AT GLASTONBURY", so this was Jay's way of getting back at him for saying that. Excellent move by Jay, and it's a good example of why he's so great.
The singer of Oasis is a straight up douchebag. Jay-Z is an amazing performer. Trust me, I've seen him three times.
It's not the first time, albeit this was on a smaller scale: "Okereke [Kele Okereke from Bloc Party] also responded critically to comments made by Liam and Noel Gallagher of Oasis in early 2007. Liam called Bloc Party "A band off of University Challenge", intending it as an insult, while Noel dismissed them "indie shit". In retaliation, Okereke stated, "I think Oasis are the most overrated and pernicious band of all time. They had a totally negative and dangerous impact upon the state of British music. They have made stupidity hip. They claim to be inspired by The Beatles but, and this saddens me, they have failed to grasp that The Beatles were about constant change and evolution. Oasis are repetitive Luddites." I do like them a bit myself though. It was a really good performance by Jay-Z, from what i saw. I watched the first half hour or so on BBC3, and during that time he performed pretty much all of the radio singles from The Black Album, Public Service Announcement, Jigga What Jigga Who, Hard Knock Life, Show Me What You Got, Umbrella and a couple others that I don't recall. I don't know if this is a regular occurence since Collision Course but he used LP samples during Dirt Off Your Shoulder and 99 Problems as well.