I agree that multiple pages currently reload after a certain time period and this is frustrating. For the most part, it reduces the advantages of having multiple pages. We might as well just keep one page open at a time, since they must reload anyways.
As it stands now, this increases the wait time to redownload the same data for a webpage, increases the traffic along the network (without the user manually hitting refresh), and overall frustrates the user making a relatively slow internet experience - slower.
As Gizmo-xl said, the data should be cached instead, until that page is closed. This could be resolved by updating the software, not the hardware. For what it's worth, I've added this suggestion to my thread named "iPhone 2008 software improvements", at http://forums.appleinsider.com/showthread.php?t=82034