All web browsers I have used on desktops etc. cache web pages: they generally won't reload them unless you ask them to. Particularly, they won't reload them simply because you used another app than the browser for a few minutes. (There are exceptions, like pages of sports scores that auto update.)
But on my iPhone, a device often is only tenuously connected to the Internet, Safari (and other apps, such as The Weather Channel app) attempts to reload the page I was looking at every time I return to it from another app! When, while writing a recent blog post, I was looking at a page listing the 100 largest television markets, I wanted to toggle back-and-forth between the list in Safari and my blogging app, to make sure I got all my numbers correct. Every single time I returned to the page listing TV markets, the page reloaded. And I am pretty sure they were not updating this data every couple of minutes! Aargh!
Does anyone have any idea why the iPhone behaves this way?