What makes you say that? I mean I always found PNG's to be very small, quick loading, & BMP quality, unlike JPGs. Whats the downside to them, other then a few lost colors, which is very unnoticable if you use a half decent program.
In addition, using FireFox, they include Alpha channelling too.
I only mentioned it because Lazarus' images are 2MB and 1MB in size, which are almost comparable to uncompressed BMP files. PNGs are only very effective for computer generated images that have a reasonable amount of flat colour. JPG produces very obvious graininess in flat colour, but this is a side effect of its compression that isn't so visible in photographs.