This is not true at all. You can generate a lot of different strongly-typed resources automatically. You just need to have a file (no, not only a text file, many file types are supported) and give this file proper name. Now, the resource will always be successfully created, but in some cases Visual Studio will generate a strongly typed resource, in other cases, the generated resource will be accessible as an array of bytes. It depends on the file type; if the system is familiar with this type, the generated resource will be strongly typed. If not, you will have to deal with the array of bytes. Typically, you put it in a memory stream and read the stream with your own constructor of your own type which "knows" how to deal with the type of resource in question.
Let me give you an example of, say, PNG image file. You should agree that this is not a text file. You should prepare such file with valid PNG content (most important item, apparently :-)), and name it in a proper way, say, "MyImage.PNG". Create an empty *.resx item, click "Add existing file" (the best option in most question; in particular, try to avoid creation of images in Visual Studio: it will force you using its editor, which is ugly; it won't allow you to edit files using in resources independently). When the file is added, it will add a copy of it to the project (with proper properties, so the file won't be copied to output directory), a reference to this file in the resource file and — attention! — will create an auto-generated C# file.
This auto-generated file will be placed as a child node to your resource file node, as presented in the Solution Explorer. Open this file in the editor. In this file, you will find the static property named MyImage (in some other cases, you will get a property with the name close to the name of your input file). This property will be strongly typed as image. The underlying code will extract it from resource and read and the image object, so you don't need to do anything like that by yourself. Just use this property in your project as some ready-to-use image. When you edit your file "MyImage.PNG" and rebuild your project, the embedded image will be properly updated.
That's all. As to other file types to be uses in resource — please see above.
—SA
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