I have a feeling that most of those searches could be answered by, "It's because you're on an unreliable internet connection".
For example, why is It that almost no site uses appcache, when it is a way of ensuring that resources are already local and the only network traffic is the truly essential part? Why do we care about retina imagery, when it is obvious that the majority of users get a worse experience as a consequence? Why have sites doubled in size in two years time without adding a meaningful percentage in content?
These all point to an industry that lacks perspective on their user's actual user experience because they are sitting on a nice fiber line two hops from the server.
HTTP caching is fine for that. appcache is more about allowing the site to largely work even after going offline. That's more than most sites need.
The reasoning behind this is a wish to avoid annoying or "unestethical" flicker from one font to another once the font has loaded.
That's great if you're on 10mbps or more.
Now put yourself on a 64kbps barely functioning link on the metro, you have DLed the 800bytes of article text you really want read 5 minutes ago but you're still waiting for that one special font which webkit requires to be able to see anything. And that wont fully load until you're off the metro.
I tell you: Lesser things can drive a otherwise reasonable person completely mad.
Don't use custom fonts on any mobile stylesheet ever. Thanks.