All the mobile browsers I've tried do this - Firefox, Dolphin, and stock Android. I distinctly remember browsing the web quite happily with Firefox desktop on a machine with 512 MB of RAM as recently as 2008, so I can't help but feel we've gone backwards.
Am I the only one who loves this behavior? I'd be perfectly happy forcing Chrome/Firefox/etc. into a 1GB sandbox and then telling it to "unload tabs on memory pressure." I only use a few tabs at a time; a simple LRU OOM-eviction algorithm should work wonders.
"From the network" isn't actually a part of the semantics of this behavior, though. If the page's browser-side cache is still valid according to its original response headers, the browser will just reload the page from cache rather than hitting the network.