Nokia has got several different display sizes and resolutions. The N97 has 360x640 pixels on a rather big display, which is a display with a average resolution IMHO, not as high resolution as iPhone, not as low as many cheaper models. I would say that the main difference is how the web browser in the phone is designed, some try to squeeze in the whole page by shrinking it, some don't.
Anyway, having different designs is a hard thing since the webswitch is far from a PC when it comes to resources
There is however always the possibility to access the different pages "frame less" by using direct page URLs, and so saving display space.