The same reason many people like myself rationalized purchasing a PS3 early is the same reason people are buying one now. I know that Nintendo Wii has made a lot of headway this generation. (Dominating the competition) and the Xbox 360 has done much of the same.
But before this generation began, I just couldn't shake the feeling that Nintendo was going to do what I felt they always do (Atleast for the past few generations) have no third party to speak of, have some really awesome exclusives but they will be few and far between. (I believe much of this is coming to pass).
As for the 360, I saw how Microsoft handled their original Xbox. I felt they had a really good plan towards storming the market. The pricing, the fanbase building in America in the previous generation, etc. However, the major chink in their armor was they legitimately "Had no games" beyond ones that existed on the Xbox. They had few quality first party developers and you could see very early on, their strategy was to steal Sony's exclusivity on games they could and combine that with their minimal first party and then they could compete with a lower entry point. The problem is, no one cares about Final Fantasy, Grand Theft Auto, etc anymore. And Halo and Fable and Gears are just blips on the overall landscape.
The PS3, Came in with one fatal flaw, it's price. I'll say it till im blue in the face. The PSN not being great initially, the relative lack of games (Which most consoles always release with) none of that mattered nearly as much as the price. The price was so astronomical compared to it's competition that you couldn't ignore it. It was one of the last consoles to release with the highest price. But the thing that has saved the PS3 is it's games. It's the same formula that Sony has used in every generation. They over-whelm their owners with game after game after game. The biggest surprise this generation in my eyes has been that the Sony first party developers (Have turned into AAA game developers) which I never remember being the case in the PS1/PS2 generations. (They always made great games, but not some of these masterpieces we have seen this generation).
In short, Nintendo isn't well equipped to dominate the console market IMHO and that is why this has been a much more all-around generation. Microsoft, just flat out doesn't care enough about it's gaming division in the landscape of their company (Atleast this generation) to staffing the amount of developers necessary to produce games for their system. Sony is in a great position (Finally closing the gap on price, with a much better worldwide brand name, previous time as a market leader, tons of first party developers and pretty much universal third party support.).
It will be interesting to see which console performs well after the new consoles hit the market. I have a strong feeling the PS3 will make some moves during that time frame (Much like the PS2) when it's cost is down.
