I don't know, I think it has to do with personalities of both parties involved as well as mindset and making a conscious decision and following through with it to be as such.
DH and I are VERY much "attached partners" and we dwelt with lots of deployments and schools, so lots of apart time. I think it helps we've always been as such, so not much help I suppose.
Some things we have always done:
Verbally express our love, adoration and respect of each other, and meaning it, often.
Touch often, not necessarily in a sexual manner, just touching. For instance, I walk by and smile at him and rub his shoulder, or snuggling up on the couch to read or watch tv, or lately he's been going by and plays with my hair on. WE have always done fly by kisses or even if we are passing each other, take time to snuggle hug and smooch (non-sexual kissing). When we sleep, even when we had a child in the bed, we'll at least have our feet touching.
Everything comes naturally to us, it's not forced, or coerced. We do it simply because we adore, admire, love, respect, and enjoy each other and love to express it often. NOW, we aren't "gross" about it
we don't get syrupy out in public, so others don't get a cavity from our love.
This works for us (15+ years and counting, and love each other more today than when we got married) , but it may not be for others.