It's kind of amazing that people have bought the "Nintendo saved gaming" thing when what they actually did was lock Sega and others out of the US market by requiring developers to sign exclusivity contracts. They didn't save gaming, they just made it look that way.
Really, Sega needs to be mentioned here because they were the first to fight against some of Nintendo's anti-consumer practices and pave the way for the rise of third party publishers and developers, which then helped to create the perfect storm of the original PlayStation. Yes, Sega laid the groundwork that Sony took advantage of much more successfully. Ironically, EA was very instrumental in that and had a positive influence on the future of gaming.
The most important thing Nintendo did was to require that code be submitted and approved for any game that appeared on their hardware. It didn't have to be GOOD but it did have to WORK. A lot of the other stuff was so that they could keep a monopoly but the code approval part solved the problem of completely broken games that plagued many of the early systems.
Sony's biggest contribution was much more simple but it also changed the industry. They went to the publishers and developers and listened to what they had to say. At the time, Nintendo dictated everything and ruled over third-parties with an iron fist. Sony went in the opposite direction, which is why they received so much support.
Microsoft's biggest contribution is that they completely embraced DLC. I doubt the entire scene of expansions, cosmetics, or even patches would be nearly as robust now without their inclusion in the industry.











