PS2 wasn't the most powerful console of its gen. Nor was PS1. Both were followed shortly by more powerful hardware. What Sony got right with them was the price, performance, marketing and software.
Thats not really true,
Panasonic 3DO : 4 october 1993, USA
http://en.wikipedia.org/wiki/Panasonic_3DO
Sega Saturn : 22 november 1994, japan
http://en.wikipedia.org/wiki/Sega_saturn
Playstation 1 : 3 december 1994, japan
http://en.wikipedia.org/wiki/PlayStation#PlayStation_.281994.29
Nintendo 64 : 23 june 1996
http://en.wikipedia.org/wiki/Nintendo_64
even if you consider the N64 as being more powerful overall than PS1 (which also is very debatable, I believe the opposiit is true) the N64 wasent launched shortly after ps1, but 1 and a half year later.
So PS1 was overall the most powerful (capable of running more impressive games engines) console for its generation.
Regarding the PS2, eventhough the xbox1 was more powerful, you cant say the same with certainty about Game Cube (I doubt game cube could run GT4 at 60fps, or JAK3 at 60 fps, or even MGS2 at 60 fps even xbox struggled with that), and with both examples, certainly the xbox and game cube (november 2001) werent released shortly after the ps2 (march 2000), its almost a 2 years gap, more than the gap in time between N64 and PS1. it means PS2 enjoyed technical superiority for almost 2 years, thats not negligeable, its no technical feat for microsoft to come out with a console more powerful after 2 years.
Concerning the PS3, I would consider it more powerful than xbox360 in terms of overall processing power (uncharted 3, GT5, last of us...) but I dont want to enter into a debate of this sensitive question...of course in some aspects xbox360 has the edge (mainly transparencies, and MSAA) but in all other aspects of game engines, the ps3 is capable of more impressive things than xbox360, thanks to the CELL monster.
Thats in terms of overall processing power, but sony had always the edge in terms of multimedia capabilities, the PS1 had an incredible sound chipset and DAC for its time and price, it was used in its time as a preferred CD audio player for audiophiles, the ps2 was also used as a DVD player, and ps3 was the best blu ray player available in the market for more than a couple of years, its also the ONLY console allowing for 7.1 lossless audio for video games.
What I mean is that hardware superiority in at least a lot of technical aspects was a signature of ALL sony consoles until now, if thats changes with PS4 I would consider it as a real surprise.