PS3's RSX was based on an off the shelf popular Nvidia GPU [1] while PS2 (the console that sold the most [2]) used a completely custom GPU[3]). It's parity on the CPU - both used a popular ISA CPU (MIPS and PowerPC) with custom additional PUs (VUs and SPEs).
As for the same hardware in Xbox1 and PS4... it depends on what degree you make the distinction. Both have AMD's SoC however other than the ISA they are very different from programmer's PoV: one is a NUMA (DDR3 + ESRAM) another is UMA (GDDR5), which is quite a difference even to a layperson when multi-platform titles compared.
My point is that while it makes a good soundbite in journalism, the availability of libraries is pretty irrelevant for a console's success.
You clearly know a lot about the details here, but from a high up perspective I think the ease of development is one of a few key factors (others being games, price, brand loyalty and features). With the PS2 Sony had a strong enough foothold in the market for developers to have to suppor the platform, and the initial under performing games to not be an issue.
If the PS4 and Xbox One were released with the PS4 being harder to develope for (lets just say flip the UMA to PS4) we would see the Xbox One with 1080p/60fps games and the PS4 lagging behind. I think this would cause the Xbox one to be on top in terms of sales.
When the first xbox was released it had a very familiar PC architecture, I think if they had gone with something bespoke it would have been an instant flop.
While it's not the only factor in a console's success I think to say it's irrelevant is an over statement.
As for the same hardware in Xbox1 and PS4... it depends on what degree you make the distinction. Both have AMD's SoC however other than the ISA they are very different from programmer's PoV: one is a NUMA (DDR3 + ESRAM) another is UMA (GDDR5), which is quite a difference even to a layperson when multi-platform titles compared.
My point is that while it makes a good soundbite in journalism, the availability of libraries is pretty irrelevant for a console's success.
[1] http://en.wikipedia.org/wiki/RSX_%27Reality_Synthesizer%27
[2] http://en.wikipedia.org/wiki/List_of_million-selling_game_co...
[3] http://en.wikipedia.org/wiki/PlayStation_2_hardware#Graphics...