Upon getting a new phone, I think many of us treat it so much better than we will, once we've gotten used to it. It's the same phone, but for some reason we treat it with special care. Some people even postpone taking off the clear film that's put over the screen, so that it appears new.
Maybe it's something I've seen in L.A., or possibly more predominantly in the Persian culture in L.A., but when they get a new car, they postpone getting their license plate put on, as to keep the sense of "new" as long as possible. I've seen instances that have lasted over a year. It might have something to do with preventing getting parking tickets, but I don't think that's the sole reason.
A new baby arrives and it needs special care, love, and attention. But, the thing with a baby that I find so beautiful is it's innocence and purity. A baby is born without flaws and it's spiritually pure. It hasn't made any mistakes in it's life and it has yet to grow and learn. It has a clean slate that many people wish to acquire, without remorse having to be a part of the process. As an adult we no longer have that feeling. As well, we must learn not to make mistakes or to learn and grow from mistakes that we've made.
A new relationship has the sense of purity as well. Everything is a "first" with a new partner. Even if you've gone to a restaurant or a theatre previously, you've never experienced it with this partner. As well, The "honeymoon" phase is all about excitement from a "new" situation in which everything is nearly perfect and it's hard sometimes to detect the flaws or red flags early on, for that very reason.
When things or situations are new, we tend to treat them with more love, attention, and care. But, it's so important to treat people and things with the same care throughout our lives. If anything, in regards to relationships, marriages, babies, family, and friends, we should not only give the same love and attention we give when it's new, but more than when it was new.
Just because a man is use to his wife, doesn't give him reason to stop the romance all together. Nor does it make it ok for a wife to be less affectionate (in whatever way possible) to her husband. An old woman can still reach over and kiss her old hubby's cheek once in awhile, just as an old, wrinkly, man can gently take his beloved's hand and gaze into her eyes. It's important to keep the love strong and alive.