I probably didn't explain my point well enough. You are completely right that it matters where you finish, although the difference is actually all but negligible.
I think the response of consumers is a great way to gauge the quality of a product. Not perfect, no, and I'm sure others attribute more weight to other metrics such as the one you mentioned, profitability. I'm a consumer and not a shareholder or accountant of these companies though so I'm more interested in this.
When I say the Xbox 360 ate into the PS3, perhaps a better way is to show these stats from VGChartz (so if anyone has better please feel free to post them)
6th Generation
PS2 (157m sales)
Xbox (25m sales)
7th Generation
PS3 (86m sales)
Xbox 360 (85m sales)
As stated, consoles enjoy real brand loyalty and this is the key part of my argument. The 7th Console Wars or whatever was not an even race to begin with. After they had such a huge headstart based on how the 6th generation went, to finish all but level is poor from Sony and great from Microsoft. I also genuinely think that if the Xbox and PS2's positions were reversed, the 360 would've absolutely stomped the PS3 in terms of, yes, this purely sales perspective. That was my point so I hope I've put that across better.
For point of interest:
8th Generation (as it stands)
PS4 (41m sales)
Xbox One (21m sales)
Microsoft have undone all of their good work from the last generation. I'll throw in a "yes, it's early days yet" disclaimer but so far it ain't looking good. Consumers simply haven't responded to their product in the way that they have to Sony's.