I don't think it's the resolution - see the BBC review, where resolution doesn't appear to be an issue on the iPhone/Touch as far as browsing is concerned.

I think you're spot on regarding the EDGE network though - it's the very reason I asked for a mobile/Internet Tablet optimised theme for this forum... a theme that is light on graphics in order to reduce bandwidth when surfing on a GPRS or even a 3G connection (3G speeds can be slow depending on signal and other factors), plus I'm currently paying per MB on my 3G connection! Any simplified layout that results from an optimised theme is also welcome simply because these devices are not desktops and still chug when processing pages with complex layouts (this includes this site - the pages load instantly on the N800 when using the Mobile II theme). One other thing I've noticed when using a dial up connection is that latency is high so pages with multiple external references (.js or .css) will take a lot longer to load due to the HTTP roundtrip, so reducing links is also advantageous (this means Web 2.0 apps could be a nightmare over a high latency connection).

I think it's good to see sites offering low bandwidth/simplified versions, but agree with others that it's wrong to label these as "iPhone" specific sites (blame the marketing boys for that!)