I think that you're right, it's easier to just vanish in a ldr. I also think it takes, in some ways, a stronger investment at first. I mean, I realise you don't have to go to places and meet, but you have to accept the fact that you will be with someone and not actually be with them. Sometimes for months before you actually meet for the first time.
For me, it screens out the "just for sex" things. I also have deeper conversations online than in a bar, typically, and form stronger connections. That might be the way I work: most of my close friends I met online, and didn't meet in person for years, my husband started as a ldr, my boyfriend and I are on a ldr right now... Actually, I don't personally have an experience of a non-ldr that worked.
So it might really depend on the person... Yet I don't think it's about the type of relationship in a distance way, I think it's about the person and the expectations.
Because I am looking for strong, deep connections, and care less about sex, ldrs work much better for me. Sure, it's easier not to form connections at all when you're online, but there is also the impossibility of close physical intimacy, and I find, as a result, a stronger occurrence of close emotional intimacy.
Because my sex drive can get me silly, and I end up going too fast otherwise, ldrs offer a "slowing down" that's very good for me.
At the same time, the relationship is "serious" from the start, in the way that we know we might have sex every few months if that, therefore the relationship is based on friendship more.
I personally find them less "breakable". As in, I find that you end up staying friends even if it doesn't turn out, because you know so much about each other already. You're usually willing to type or write (if you write letters, which I always love doing in ldrs) more personal things than what you'd say. Again, that might be just me.