Besides: Paint.NET is able to open tiff files, doesn't matter how they are compressed. So the several algorithms are implemented anyway. It seems to me that it's only the GUI, that does not support a sophisticated "save as", isn't it?
... not high priority for Paint.NET - but indeed it's an important fileformat. I was happy for having fount an imagesoftware that did not affect the common and the private tifftags when manipulating the image. Unfortunately (important for my daily work) I'm not able to select another compression algorithm than LZW when save the new tiffimage.