th (table header cell) has not been deprecated

Two programmers I'm working with seem to not know what th is or how to use it. One went so far is to put a div with a class in order to make something bold. The other only used an h2. Why they couldn't use th and changed text alignment in css is beyond me. Note that all of these contained headers and th is specifically used for table header cells.

Both of them also used span and div with a class inside td instead of just assigning the class to the td. Again, no idea what the logic was.

Another pet peeve is assigning a class to every single child of an element instead of assigning a class to the parent and using inheritance.