Of course a V12 has 12 pistons.... but it doesn't mean it has 12
of everything else in it 
Each cylinder must have 2 valves at least, 1 intake
and 1 exhaust. So a typical 4-cyl engine will have 8 valves and it
can go as much as 20 valves, 5 per cylinder (2 intake, 3 exhaust
etc).
