I'm of the opinion that what works for some people just won't work for others. I think everybody ought to do what makes them most comfortable as a couple and that can vary widely.
My bf and I started dating about 9 years ago - I was 18, he was 24. At that point our life experiences were very different; I was just starting university while he had finished school and had been working for several years. I had never lived outside my parents' home but he had lived on his own and/or with roommates for over five years.
Due to these differences, as well as my ongoing focus on school (and a desire not to derail my education with a bad breakup should it have occurred), we gave very little thought to moving in together for many years. I was also insistent (and he agreed) that a little life experience (living with roommates etc.) would be to my benefit so I spent a while doing that while he continued to live with friends. I think that experience (as limited as it was) was good for me and has probably helped our relationship quite a bit. It has also reassured me that I can live by myself if our relationship ever goes south.
(And frankly, after seeing the state of certain friends who feel they can't exist without their exes...I'm REALLY glad for the life lesson.)
We have now lived together for just under 2 years having waited for about 7 to move in with each other. In spite of the fact that we had been dating for 7 years, the first year of living together was a challenge. (Two completely emotionally independent people, unaccustomed to seeing each other every day, thrown together and forced to live in the same space is SO NOT PRETTY).
I'd like to say we've gotten over it...but on some days, we're still adjusting.
While we have discussed marriage off and on (recently with more seriousness than before), neither of us is in a rush to do that. I'm currently still in school and we don't want kids so marriage isn't a priority. I'm not sure if we're one of the aforementioned couples that gets comfortable cohabiting and never gets married. Maybe? LOL (In all seriousness, we'll probably get married. But I don't think either of us cares about the ceremony part. Just the party part. Maybe we'll just throw a party.)
In the meantime... I think we're good.