Microsoft are a big company yes. Something of an exception, and actually I'm very pro Microsoft (despite lots of analysts writing them off). Most think they will be overtaken over the next 10-15 years though. Tech is a bit of an exception though (due to huge margins). Go and look at the top 30 companies in 1990, and how many of them are in the top 30 now.
As for 2005. Arsenal were the best team in the league. They havent won it since and are currently 19th. City were still un the championship, they are now the dominant team. Italian teams dominated the CL, they are now also rans. Liverpool have gone from 4th, to 2nd, and then nearly went bankrupt before re building again.
The one certainty of life and sport is things change. It's actually very hard to stay at the top for prolonged periods. I sense Chelsea and City will manage it while they have shareholder investment. United have huge cash reserves. Outside of that, not really sure on the rest.