Honestly, I think defining it as "Success" or "Failure" causes unnecessary arguments and prevents people from seeing the point ...
Being that people tend to favour products that are associated with trusted and popular brands, Nintendo and Microsoft have improved their position for the rest of this generation (and the upcomming generation) by simply increasing the number of people who have bought their systems; at the same time I think most people will accept that Sony has an uphill battle to sell systems to 1/2 the people who bought a PS2 and thus they have degraded their position in the market.
The other consideration is growth of the company/division and the increasing value of the IPs the companies hold (and are able to produce). The unrivaled profitability of Nintendo, combined with their ability to increase the sales of their software (generation over generation), has given them the ability to aquire (and organically grow) the number and quality of their developers and has increased the value of their IP portfolio. In contrast, Sony is struggling to approach the sales they achieved with the PS2 and has been bleeding money; this combines to mean that the value of their IPs is shrinking and they will have difficulty maintaining the number and quality of their developers.
