It's interesting to note that the figures they are talking about-- market share-- refer to current sales, not installed base.
The Xbox 360 launched nearly five years ago, in November of 2005. The PlayStation 3 and Wii launched a year later, in September and November of 2006 respectively.
Nearly four years later, monthly sales figures for the PS3 have just now reached parity with the Wii and the Xbox 360. That means that until this point, most months the installed bases of the other two consoles were still growing faster than the PS3's was. The PS3 could be said to have been catching up in terms of monthly sales, but in terms of installed base, only falling behind more slowly.
If things were to stay like they are (unlikely, of course) the installed bases of each console wouldn't change relative to each other: Wii in first place, Xbox 360 in second, PlayStation 3 in third. As long as sales remain at parity this is what would happen.
Even if PS3 sales continue their growth and surpass the sales of its competitors from here on, if the rate of increase does not change radically, one might assume that it could take anywhere from one year to as long again (four years) before the higher PS3 sales translate into an actual advantage in installed base-- which might be another four years from now, making the PS3 and the Wii eight years old and the Xbox 360 nine years old.
If one admits that at least for MS and Sony, the real money is made on games and accessories, then the important figures are installed base over time, since the more people own your console and the longer they own it produces more opportunities for sales of games. If, for instance, Sony's worldwide installed base were to surpass the Xbox 360 and then the Wii in the same year the next generation is launched-- or indeed, perhaps any date no earlier than one to four years before the next generation launch-- the victory might well be called pyrrhic. If Sony keeps its worldwide installed base advantage for only a small percentage of the lifetime of the generation, then it incurs little or no advantage.
After sales market share of console units, the next important thing to look at will be when AAA cross-platform titles generally reach parity between Sony's platform and Microsoft's. (There are few titles that span all 3 consoles this generation and I'm not entirely sure there's an equal competition for those sales even where they do.)
One can only speculate what the situation now would be like if the Wii had a more extensive third party development ecosystem (as the 360 has) or if the Xbox 360 had not been plagued with terrible hardware reliability problems.
It's definitely good news for Sony, but with a lot of qualifiers.