I think that's a safe assumption. Anecdotally though, I prefer to stick with one service and if I was offered options that didn't include my primary choice I might be reluctant to sign up. I just don't think that intentionally walling out a group of potential users is a great idea if you're trying to expand your audience.

I tried to quickly find some numbers on distribution between them. Although I didn't find anything concrete, it seems to be Facebook > Google > LinkedIn. I would actually love to know more about this. Maybe someone with more experience has some more data?