Well for the one top ten web site that has open web logs, mobile traffic does seem to be taking off at the expense of desktops - http://www.vartmp.com/blog/2013/04/16
This chart says nothing about whether mobile is eating into the absolute traffic that desktops are getting. More likely mobile traffic is increasing a lot, and desktop is holding steady.
Feb 2012: http://stats.wikimedia.org/archive/squid_reports/2012-02/Squ...
Feb 2013: http://stats.wikimedia.org/archive/squid_reports/2013-02/Squ...
More data needed.
Agree on the more data needed.