However, there are three things that can break strings, and do, and the treble seems to be a bit more sensitive: the first is "prepared" pianos, where for various reasons people add nuts and bolts or screws or other oddities to the strings to make particular sounds. Don't laugh; it's done. The problem is that these can knick the string, and create a weak point -- which will break.
A side note.One music prof I know also had concerns about the potential harm of preparing pianos could cause. So a tech was brought in to witness and scrutinize the complete process of preparing a piano. The response from the tech was clear: strings undergo far more stress during installation as compared to following proper procedures for preparing a piano. If one takes care with the preparation, there should be nothing to worry about.