<p>With all the fuss about opensource projects, how come there is still not a strong standard that enables you to make portable code (I mean in <code>C/C++</code> not <code>Java</code> or <code>C#</code>)
Everyone is kind of making it's own soup.<br><br>
There are even some third party libs like <code>Apache Portable Runtime</code>.</p>

I think the main reason there isn't any single library anyone agrees on is that everyone's requirements are different. When you want to wrap system libraries you'll often need to make some assumptions about what the use cases will be, unless you want to make the wrapper huge and impossible to work with. I think that might be the main reason there's no single, common cross platform runtime.
For GUI, the reason would be that each platform has its own UI conventions, you can't code one GUI that fits all, you'll simply get one that fits just one or even none at all.