I would agree with the OP. I've always felt that, if you were prepared to go through all the problems and trauma of suicide, then you would be easily able to cut yourself off from the world you know in another way.
If you feel trapped, there are so many ways out. Just up and disappear for a while.
Sadly, I think once people starting thinking suicidal thoughts they are usually at the point where they have so limited their ability to do anything that this message wouldn't get through. They'd get as far as step one (booking a plane ticket, maybe) and then give up. Because I guess somewhere they don't really feel they are worth it.