PS1 was called PSX long after its release. I think the local version of the official Playstation magazine even called it PSX. Whether I remember correctly or not, I do remember at least some magazines calling it PSX. My point is simply that it was a common name, and it's the name I used to call it when abbreviating.
Threads like this make me want to call it PSX again, despite not all people understanding what I mean then...