In the US this is a fire code issue. Doors need to swing inward to avoid people getting trapped inside from outside obstructions.

edit: I seem to be misinformed about firecode. I may also be over extrapolating from what I know about bedroom doors as well. The general idea of obstruction is more valid there. It seems the more common reason bathrooms would not be allowed to swing outward is obstructing the minimum width of hallways.