It is "smart" enough. Before and then during searching the problem space the solver performs constraint propagation, which is a bunch of clever algorithms (the maths for I am yet to grok) that reduce the domains of variables. This allows it to reduce the problem space to something reasonable.

So why 10? I guess I was being lazy! But you are right I will do an update with some more in the domains.

http://en.m.wikipedia.org/wiki/Constraint_propagation