Maybe "tires" are different where you are - but where I live, they wear in the tread centre if over pressure or on the tread shoulders if under pressure - they have done for all of my 50 years driving.I think that's too broad of a statement.
If a specific cross section (size) tire is mounted on the correct width rim, it shouldn't "bulge" out in the center as per your statement above when it is designed to run max pressure of 50psi (for example) and you run it at say 40psi vs the 33psi that's on your sticker. Now take that same scenario and mount it on a 6" wide rim instead of a 8" wide rim and you'll have a different story.
But there are many other factors, such as road surfaces, driving styles, vehicle condition, loads, etc. Everyone needs to understand that stickers are only suggestions and don't apply to all conditions, makes and models of vehicles, etc. Monitor your own situation and requirements and adjust as necessary.