Only??!! I know other guys may play more tournaments but Roger, for example, plays 17 or 18 tournaments each year. That is the norm for him not a reduced schedule.
Basically you're saying he should play all the slams + all the mandatory masters 1000 + MC + a couple of 500 + a 250, that sounds like a pretty normal schedule to me.
Looking at the ranking as of now:
Top 4 - 19+, Djokovic
5-10 - 22+
11-50 - 20+, Haas
51-100 - 18+, Karlovic
Yes, I would call playing 18 tournaments a year a reduced schedule. It it were to be a normal schedule, he would be playing around 22 to 24.
DTT(D) : 2012 Nice & Eastbourne, Olympics Bronze, 2013 Indian Wells w/supertec
PAW : 2012 Atlanta
Suicide: 2011 Barcelona*, 2012 U.S. Open*, WTF*, 2013 Gstaad, Winston-Salem*
TT(S) : 2011 Szczecin CH, 2013 Miami & Stuttgart
TT(D) : 2011 Eastbourne w/Blarghman, Pozoblanco CH w/MuriloBrasil, Genova CH w/ESimp, Szczecin CH w/Dexter,
2012 Newport w/chowdaheads25, 2013 Memphis & Stuttgart w/Blarghman
FITD : 2011 Kuala Lumpur, 2012 Kitzbühel, 2013/14 Monte Carlo