Just felt that adding 14 extra constraint validators and their tests for fringe and corner cases was unnecessary.

I don't think the number of validator instances matters. Maintenance of constraint validator instances is quite easy (leaving the more controversial constraints like Email, URL and SafeHtml out of the picture). Most of them we wrote once and never had to update. Is there no common base class to unify things? With JodaTime this was for example the case. Not sure what the new Java 8 classes look like though.