Interesting site - but it looks like it has only been around since 2010.

http://httparchive.org/trends.php?s=All&minlabel=Nov+15+...

Small amount of time relatively speaking (the Guardian example was from 96 through 2011). So the general trend for a bunch of sites (on httparchive.org) looks more-or-less linear, but that's probably because only a limited amount of time (2 years) is in view.