Why did the PNG site use only GIFs for so long?
It didn’t! Ever since the first HTML 4.0 drafts came out, the PNG pages were modified so that virtually all of the GIFs most users saw would have been PNGs had their browsers supported the HTML 4.0 OBJECT tag correctly. The basic idea was to wrap an OBJECT PNG around an IMG GIF or JPEG; old browsers would see the GIF or JPEG, but new ones would see the PNG–no broken images for anyone. (After all, the primary purpose of the PNG site was and is to be informative rather than political; in other words, the emphasis has always been on making it useful and functional for everyone, regardless of one’s choice of browser.) Unfortunately, Microsoft, Netscape and most other browser vendors implemented OBJECT so poorly that the tag is still virtually useless for new image types, even as late as mid-2000. Forget about backward compatibility; even current compatibility is abominable! (Notable exceptions include Amaya and Mozilla.) See this page for details about the OBJECT tag and the browsers page
