Why Skype is so popular?
Very simple… they do just what they are supposed to do! Provide instant messaging. And, they are best advised to stay that way. Google Talk, Yahoo Messenger and the like are great deals, but most of the people who have the need of IMs have more than one account on those systems. We think no further elaboration is needed 
this tells me nothing about why skype is so popular!! honestly
You didn’t read the post properly. They excel at providing one function – Instant Messaging, period. They don’t try to be jack of all trades.