The point is that PNG/MNG are superior file formats in every way. Smaller, more adaptable, more features, etc. So, for future development it makes sense to use and support PNG/MNG rather than GIF. Whether there are existing sites still using GIFs is totally irrelevant, thre's a good chance the webmasters on a lot of those sites aren't even aware of the royalty issues involving GIFs, or that PNG/MNG is around and are altogether better file formats. Even if they do, depending on the number of images stored, the storage method, and the competency of the webmaster, converting all the image files on a single large site could be a very time consuming ordeal.
Very few open source and free programs still have GIF write support. You can argue all you want (and I'm sure you will) that commercial programs are far more popular, but that simply isn't the case. With a huge proportion of programs being developed without GIF support, and huge open source backing for the PNG/MNG formats, there can be little argument that GIFs are on the way out and PNG/MNG are on their way to the top.
