Hamlet and Eggs

From Hamlet, Scene IV

HORATIO:

Is it a custom?

HAMLET:

Ay, marry, is’t;
But to my mind, though I am native here
And to the manner born, it is a custom
More honour’d in the breach than the observance.

What does this closing line really mean? In the political and policy circles of my acquaintance, this expression tends to be used differently in the U.S. and the U.K.

In the U.S., I mainly hear this expression used to mean “A rule that is broken more often than it is followed”.

In the U.K., I mainly hear it used to mean “A rule that is more respectable to break than to follow”.

On a separate note, people use “to the manor born” — perhaps originally a play on Shakespeare’s words — to indicate that someone is from a wealthy family (see the popular TV show here). If someone like that marries a poor person, is that poor person “to the manor borne”?