The chances of such a file coming into existence accidentally and also being picked up in the find filter seem slim. If it's around maliciously, I think you have bigger problems. Anyway, there are many other failure modes of rm -rf that are a lot more likely and you should worry about.
The chances of such a file coming into existence accidentally
When sharing servers with less UNIX savvy developers you will observe A) a notoriously polluted home-directory and B) plenty of files with funny names such as -, * , user@server.com (from failed scp attempts) all over the place.
It's indeed relatively hard to create a file called '/' by accident. But I've seen files containing the '/' along with spaces, which can be just as deadly. Oh and the popular * -file is not to be taken lightly either.
As a rule of thumb: Learn the safe way to chain these commands (find/xargs in particular) once and stick to it. And always perform a dry-run before launching the real deal.
Unix filenames can not include / characters or null bytes, so I call shenanigans. Nonetheless your point stands: be careful. (And make liberal use of -print0 !)
