I still think it's the Sega Genesis that pioneered it. The Genesis is the platform that popularized sports games like Madden NFL and FIFA.
People also maybe were too young to remember, but the 16-bit wars were incredibly brutal, lol:
http://www.youtube.com/watch?v=qZqNxv8NofY
But I think partially a lot of this had less to do with the companies themselves and simply with kids getting older.
If you were 10 years old when you got an NES, and pretty much every 10 year old in North America had a NES in their living room, that made you 12/13 when Mortal Kombat hit the Genesis, and 16/17 as the Playstation started to rise. It's really not a coincidence that your tastes in music/TV/clothing would start to change a little, why not gaming as well?
Mortal Kombat too IMO put hyper-violence in video gaming on the map and was the first violent gaming blockbuster.
