There's so many reasons for their sustained successes. They've basically nailed it in terms of console design and marketing every generation they've entered and they always make sure they have a massive gaming ecosystem - they cover all genres as well as extra media capabilities to give their consoles a mass-market appeal.
I'm a huge Nintendo fan and always have been but Sony came out strong with the PS1 choosing the right media format as well as making the system easy to develop for. Compare that with the N64s cartridge format and Sega absolutely ruining any chances they had of making a dent in the market set them up for the win that Generation and they've been on top since.
Sony are smart with how they approach each gen. The PS2 absolutely steam-rolled the competition in the 6th gen because they made it backwards compatible and included a DVD drive in the system knowing that that would be the next big home entertainment format. People literally bought the console as it was the same price as DVD players (cheaper in some cases) but could play games as well making it a no brainer.
The only 1 time they got it wrong (with their home consoles) was with the PS3 which was seriously overpriced and hard to develop for. You could see their idea of including a Blu-ray player in it as that was the next step up from DVDs but unfortunately for them Blu-Ray never became as popular as DVDs (the jump from DVD to Blu-ray was nowhere near as big as the VHS to DVD jump so not everyone felt the extra cost was worth it).
There are other factors I could go on about such as the fact they tied down many developers and purchased studios over the years giving them great exclusives. This has kept them a step ahead of Microsoft as the Xbox competes with PS on a technical scale but not in its library. Obviously Nintendo do their own thing now and focus mostly on portability which is a market Sony and Microsoft aren't able to compete with them in.







