Resource file (.resx) vs reflection to access an embedded resource

I may be missing something very simple here, but what's the benefit of using reflection to retrieve an embedded resource from the same assembly that contains the resource as opposed to simply retrieving it via an .resx file? I see this a lot but don't get it - is there a reason to use Assembly.GetExecutingAssembly().GetManifestResourceStream(resource) compared to resx file Resources.resource? Even Microsoft does it: How to embed and access resources.

What I mean exactly: suppose I have an assembly MyAssembly that contains an embedded resource Config.xml. The assembly has MyClass that implements a method that returns said resource as a string:

public string GetConfigXML() // returns the content of Config.xml as a string

Often, I see this implemented like this, using reflection to retrieve the resource:

public string GetConfigXML()
{
    Stream xmlStream = Assembly.GetExecutingAssembly().GetManifestResourceStream("MyAssembly.Config.xml"); 
    string xml = GetStringFromStream(xmlStream);
    return xml;
}

Why use GetManifestResourceStream() when you can:

1. add a resource file (Resource.resx) to the MyAssembly project in Visual Studio;
2. add Config.xml to the resource's 'Files';
3. get the content of Config.xml in a much simpler way: string xml = Resource.Config;

I don't know how Visual Studio handles .resx files internally, but I doubt it simply copies the resource into the .resx file (in which case you'd end up with duplicated resources). I assume it doesn't use reflection internally either, so why not simply use .resx files in situations like this, which seems much more performance-friendly to me?