There are only like three or four that aren't just flat buttons with a different border radius and colour. If this had been done in the mid 2000s it would have hundreds of entirely different looking buttons. Glassy buttons, metal buttons, glowing buttons, pixel art buttons, cartoon buttons, etc.
Lack of consistent system-wide UI and UX was my biggest gripe with GNU/Linux/X11 back in the day (‘90s, pre-Winamp era, other OSes had most apps with uniform look-and-feel) while I still cared about things like that.