As I see it, that question comes from people who are fluidly flexible with technology. That is, why not just dump Skype, and use Hangouts because, well, Hangouts are better. Uh.. sure. Maybe Hangouts are better but ...
I don't want to get into a my-app-is-better-than-your-app argument. If we back up a few feet to get some perspective, there's an interesting issue here.
People have their preferences, and some people are more flexible than others in adopting something new. It doesn't matter whether someone is old, or young, or male, or female, some people are inflexible, others are flexible, and one person might be flexible about some things and inflexible about others.
There is an existing culture of Skype usage, and some people have Skype built into their business practices. That represents a cultural inertia preserving Skype as the status quo.
I myself may be readily willing to adopt Google Hangouts, but if all my friends want to stay with Skype then I'll be awfully lonely.
Similarly there is an existing culture of using Microsoft Office to create real Documents. Most publishing houses demand manuscripts in Word format, for example. Therefore, no matter how much I despise Microsoft and their feeble attempts at software, if I were to write a book the typical publishing house will ignore me until I can write the book using Word. Google Docs is not sufficient, today, to replace Word for those who care about the details. At the same time there are zillions of people doing simple tasks in Word, for which Google Docs would be sufficient, but don't want to switch because they're accustomed to the way Word works and don't want to switch.
In other words there is a difference between a "need" and an attachment to a specific tool to fulfill that need.
If the need is "video chat with friends," Google Hangouts is probably a perfectly fine tool.
If the need is "video chat with ____" and that person only uses Skype, that's an example of a strong attachment to a specific tool. It would be nice if that person were to be flexible and switch from Skype to Hangouts, but they may be inflexible. Therefore it would be nice if the Chromebook ecosystem were flexible enough so people could install Skype.
The attachment to a specific tool is the inflexibility - or inability to switch tools. But is it not also inflexible to stick to "Hangouts is superior and everyone else should dump Skype for Hangouts"?
As it stands, the only video conferencing app for Chromebooks is Google Hangouts. As Chromebooks become more popular, rising pressure may force Skype (the company) to develop Skype for Chromebooks, just as they had to develop it for iOS and Android devices. But at the moment Chromebooks are essentially taking that stand, proclaiming that Hangouts is superior over everything else.
If there were a Skype app for Chromebooks then I wouldn't be writing this blog post, I would have just installed it and gotten on with life.
Chromebooks, as they stand, do not fulfill every need. It can only provide tools that run inside Chrome. While the Chrome team is rapidly improving its capabilities, there's a big pile of existing apps written in native code for specific platforms, and which would be difficult to port into a web browser. JavaScript performance is rapidly improving, but it is a limiting factor in some application types over native code apps.
It means that while there are adequate replacements to use inside Chrome for many kinds of applications, not everything is supported. Meaning you have to carefully evaluate your needs. The method is to install Chrome on your regular computer, and live solely inside Chrome for awhile. The longer you can make it before escaping out to a native code application the more likely it is you'll be able to adopt a Chromebook.