You're thinking far too narrowly on this one.
The point, IMO, is that the PS3 has yet to have mass market compelling titles. It's absolutely the case that there are 10's of millions of folks who have yet to go "next-gen" and this title is one that will get many of them there. While it will certainly have a positive effect on both the 360 and the PS3, it will have a positive effect on the PS3. No mention is made that it will affect the competative slant (by itself), but it will be more significant for the PS3 market than the 360 market from an adoption standpoint as the 360 has already had multiple "system selling" titles (GOW, Halo 3 as the biggest).