These numbers are highly questionable. I have no idea how they come up with these numbers. Real Madrid, Barca and Man U worth over US$3bln? haha I don't think so.
Who would pay that kind of money for a business that doesn't make money. They may make a profit from time to time, but over the cycle they are break-even value destroying businesses that relied on capital from their founders to keep prospering.
Take Juventus vs AC Milan. According to Forbes AC Milan is worth 990m. Juventus is not on the list, but the market capitalization fo Juventus is only 250-300m last time I checked. I believe Juventus is in better financial shape than AC Milan and has a fan base which is similar to better.
Being listed in this case, shows the true value of your business than some speculated number Forbes has come up with.
What I do know, is that in Europe, Juventus as of last financial year ranked 8th in terms of Revenue. I would curious how it ranks once this financial year's numbers come out. My gut feel is that we may go up a place or two.
By the way, it is true that the US ADRs for Manchester United are traded in New York and it shows up a market cap of US$2.8bln which respesents a current PE of 100x and forward PE of 50x. That is an extraordinarily high multiple but at least they do make money.