I kind of think it's a bit of a combination. Sure, they are getting older, but I think if you've been together that long, once the one goes, the other kind of stops fighting so hard to hold onto life. You know, my dad didn't tell me he was being kicked off the ranch where he had lived for 84 years. His dad had sold the land when they were going bankrupt. He kept the mineral rights, but sold the surface to the coal mine, and then leased it back to live on and have his cattle. My dad took over the ranch business when his dad died. Then, my dad gets a letter at 83 years old that said they wanted to start digging and he and the cattle would have to go elsewhere. He did nothing to prepare for the move, and a couple of months later, he was gone. I feel like he gave up. He didn't WANT to have to start over at 84 (he turned 84 the week before he died). He had known no other life than the one he had on the ranch. I think he just said "to heck with it. I'm done" and just kind of let go. And because of his age, his body was ready. But I do think there's a link.
My brother was at the hotel sleeping when my mom got really bad and we called him to come back to the hospital. We had spent the night at the hospital. She started bleeding from her nose, and she had the "death rattle", but she held on until all 3 of us (my husband, my brother, and I) were there and I told her we would be there for each other and if she needed to go, she could, and she immediately took her last breath as soon as I said that. So I'm convinced that, at a certain point, you're body is ready, and if you just give in and stop fighting it, you go. And if you've been holding on that long, and then the person you were holding on for goes....I think I'd give in, too.