umm.. what would you ever need 8 buttons for??
the most any game requires at once is 6, and some people like the neo geo layout to be correct so i see the reason for 7. but 8 is just useless to me, could you explain why you would need a 8th button?
These two controls are designed to be hooked up to consoles like the PS2 and XBox. For them, you need 8. I assume if you wanted to run console emulators on your MAME machine you might need 8 buttons as well.
Oh, and Ultimate Mortal Kombat only needs 6 buttons like Street Fighter 2, but the button layout is different. SF2 has two block buttons, UMK3 has 1 block button and 1 run button. If you wanted to play UMK3 on a standard SF2 layout, you'd have to have the run in the middle of your button layout. That's just inconvenient. So I guess to really play SF2 and UMK3 properly, you'd need 7 buttons.