Remember a time when the consoles were cartridge based, well the next step was going to disc and Nintendo seen Sony had made a cd attachment already decided to partner up with Sony however when Sony advised Nintendo they in the future were going to release there own console they thought Sony would have an advantage of knowing both Sega and Nintendo hardware and decided to allow Sony to announce they were going to make this attachment only to have Nintendo re buff it, and we all know Japanese and how they don't like to shamed. Well they decided to open up the vaults buy some software companies and made the Sony PlayStation. Things were down and out there for awhile for the great Nintendo the N 64 sold approx 35 million to Sony 100 million and Sony has never looked back, however in Nintendo's favor they did bounce back with the Wii and made it the number one selling console again, but you notice Sony competed with Nintendo since that day, Nintendo had the game boy line Sony brings out the PSP which sold 70 million and are bringing out the Vita to compete against the 3DS. Also in that time Sega was replaces by MS as the third party. For many a years it was ps2 xbox then the GCN at least going to the bottom forces innovation or failure usually.
Ever since then I know of people who will only play Nintendo the same of the sony, I personally just like taking advantage of the products these events bring to us the consumer, its unreal the back stabbing and what not that has happened in this industry,
Here are some links for some informative videos
Sony Vs. Nintendo - YouTube
Rise of Nintendo - YouTube
SEGA Vs. Nintendo - YouTube