Correct. A cursory glance at the data used for that graph http://stats.wikimedia.org/archive/squid_reports shows that desktop traffic has actually increased significantly in that time period (+ 25ish% for both windows and mac). For example:

Feb 2012: http://stats.wikimedia.org/archive/squid_reports/2012-02/Squ...

Feb 2013: http://stats.wikimedia.org/archive/squid_reports/2013-02/Squ...