Shiv, what you've said is absolutely right and that is the reason why I like T20. You can hardly see a test or an ODI game ending in an upset. Even in ODI, it occurs at times but I've never seen it occur in tests. I'd say that England, Australia, Sri Lanka, South Africa, New Zealand and unfortunately, India are all on par with each other. But on the other hand, I hardly see teams like West Indies or Bangladesh or the Netherlands winning matches. In T20, that doesn't happen. Nothing can be taken for granted. In World Cup(50 over), generally, in group stages the contest is "which test playing nation comes first and which test playing nation comes second". I was wrong in only one prediction, ie Ireland vs Pakistan(being an India hater, I definitely predicted Bangladesh to win).
So, I like T20 because it is almost like football. No result is certain. Most people consider England winning the T20 World Cup was a huge upset(which I don't, obviously).