As the owner of a fairly big website (around 100 pages) I can answer that. Simple matter is that GIF is a much smaller format allowing pages to load quicker. The big downside to GIF is the quality of the image where more than 256 colours are present and at times even the ballsy Photoshop cannot dither enough to smooth out transitions between colours, which is where PNG comes in. We all know that PNG is a far better quality format and for photographs it craps all over GIF three times over but where possible most webmasters still use GIF where it is possible to get away with using them. Having said that I still use JPG alot for photos through force of habit though have been known to use PNG at times and will probably use it more often as time goes on. One thing is for sure though, if you are right when you say that PNG is now the standard, webmasters are being dragged kicking and screaming to use it. It is definitely a very good format though, better quality than GIF and better quality than JPG.
