You miss the bonding with your SO. You miss out on the time to talk before you fall asleep. you miss out on the gentle touch of a hand on your back as one person is reading, you miss out on cuddling in the middle of the night, you miss out on the joy of waking next to someone you love in the morning.
I am sure someone will come back with "I miss the snoring" or something, but of course you can fix that. Each their own, but you are removing a huge part of your married life by not sharing a bed.
Why not hop in the car and drive down the road and stay in an apartment or a hotel room? doing the same thing by staying apart. Yet that idea would be crazy....
Why do you assume most of those things can only happen by people who sleep--that's sleep, not cuddle, or watch tv, or read, or talk--in separate bed/rooms? And why do you think that people who do sleep in the same bed automatically do all of those things you mention?
My wife and I do sleep in the same bed (king size thank goodness), but go to sleep and wake up at hours apart. We don't technically have talk time before *we* go to sleep. She comes and cuddles with me and we chat before I go to sleep around midnight. (Sometimes I'm too tired and I just roll over into my sleeping position and she gets the message to stop trying to have conversation.) I don't see why people who sleep in different beds couldn't do the same thing.
Neither of us ever read in bed except when we are ill. So there is no touching of either of our backs by the other. We don't have a TV in the bedroom either. Basically we sleep--literally sleep--in there, sometimes cuddle there, and have sex in there. Reading, tv watching, spirited discussions, and more cuddling take place on the couch or in the shower.
We also never cuddle in the middle of the night. She has sleep apnea and it takes her a long time to fall asleep--plus she often has to move the dog out of her spot on the bed--so often she does interrupt my sleep when she comes to bed. Sometimes when she does I apparently sit straight up and give her the death stare. I never remember doing so, so I must still be partly asleep when I do it.
I do wake up next to the person I love each morning--but she doesn't. I get up 3+ hours earlier than her. I don't see why it matters if she's there or not. I've got the dog whining to go out and after being awake five seconds the feeling of my really full bladder kicks in and I'm out of bed in two seconds to take care of those things. Often if I'm home a few hours later I'll go climb back into bed with her when it's time for her to wake up and we do some cuddling then. Again though, people who sleep in different beds could easily do that too.
So is my marriage a strong one since we do sleep in the same bed? Or is it one of those horribly weak ones because we don't read in bed together and I'd rather pee first thing after waking up then bond with my wife?
Like other people have said, my parents have slept in separate rooms for about 25 years (married 30) first because of kid's with sleeping issues and now because of snoring, light sleeping, etc. As far as I know, possibly the rockiest time of their marriage was the first 2 years--the only years when they slept in the same bed--when they almost divorced. Now their marriage seems to be the lowest conflict it's ever been (I think it helps A LOT that the kids are grown and money is much less tight). When I was a teenager and up later than my parents, their pattern was around 7-9pm they went in the bedroom in their PJs and shut the door to talk/watch tv/whatever. Then around 11-11:30--often after my dad had fallen asleep--my mom would leave that room and move to the other room.
Not sure what they were doing in there for hours, but I'm guessing there was an awful lot of time for touching each others' backs if they so desired, no?
I stare at the clock counting down the minutes til he goes.. someone might find that sad but its true. 
