I don't know if this is completely true since I don't have the means to verify its veracity, but:
Did you know that combos in fighting games is an example of
serendipity?
I read somewhere that combos began as a programming oversight in the first Street Fighter II (IIRC). It was not the intention of the programmers for combos to be possible (or, more precisely, they did not deliberately program support for combos), but due to how the program was written, combos were possible by "mistake" (in other words, hitting the opponent while his previous "got hit" animation is still going on, thus without the opponent being able to react to it). In a way, it was a bug. However, it resulted to be such a cool feature that they left it. Combos have since then become such an ubiquitous part of fighting games that a fighting game without combos is practically unthinkable.