There's no disagreement here, actually. I personally find them preferable to .jpg, given a choice, and while generalisations are dangerous (it's often possible to disprove a generalisation with a very specific, perhaps unlikely, example) I find .png files tend to be smaller "live" than a .jpg file which isn't visibly poorer.
Which is great, for "live" use asuch as on the web.
Ian (and I think others) however are saying that .jpg files compress further in .zip or .rar form, so that - in a compressed archive (such as a game bundled with graphics and sound) .jpgs of visibly similar (possibly "identical" to the eye) quality actually end up taking less space - which makes them lighter to download. which is a good thing, overall.
It's all horse for courses - there's no "one good way" to do everything, each method/type has its pros and cons
