Only Federation ships have them. Most do, anyway. Miranda, Constellation excepted, maybe a couple of others.
But don't these exceptions suggest that navigational deflectors could also be shielded from our view (same goes for alien vessels) and don't necessarily have to look exposed like they usually do on the Enterprises?
In some of the original TOS pre-production sketches of Matt Jefferies the main sensor-deflector of the Enterprise
was covered by a dome, suggesting that a cover doesn't necessarily inhibit the performance.
Alternately, assuming the Miranda and Constellation Class vessels have automatic anti-collision programs the sensors could detect objects on a collision course far ahead and correspondingly alter course.
Alternately, this distinct bow feature on all Enterprises
could be a unique device, enabling these ships to emit a strong deflector beam others cannot.
We have seen this "unique" (?) feature been in use in "The Paradise Syndrome" (TOS Enterprise attempting to deflect asteroid to alter its course) and, of course, in "Best of Both Worlds II" as a weapon in an attempt to destroy the Borg cube.
Of course, those two examples involving the use of the navigational deflector just illustrated how useless the deflector beam was in those particular cases.
And maybe that's another reason why we didn't see more Constitution Class starships in TNG. Why continue to keep an outdated starship design with the extra burden of an engineering hull just to have a place onto which to stick a huge but useless navigational deflector...