I was browsing through the web and I came across this sentiment:

> 
> Dear Skype, this (red X) button means close, not minimize
> 
> 
> 

I also found the same [question on the Skype website](http://community.skype.com/t5/Idea-garage/the-X-means-close-not-minimize/td-p/1523929). Why would a company like Skype do something that is so different from the standard? Microsoft Lync (office communicator) also has this design of using `X` to minimize. 

What user experience reasons could cause such large companies as Microsoft and Skype to choose a non-standard behavior for the `X` button?