I don't think it will directly effect PS3 sales but it does bring a consistency to the brand recognition which in the long run may help sales or may not. However it is always good to have a consistency with your brand.
The reason Sony did this was, as they stated, that the Playstation3 logo on tv was often times unreadable from a certain distance where as the much shorter XBOX360 was big and stood out more on commercials that were multiplat. Because of this they shortened the logo to PS3 so that it could be bigger and more readable and thus they decided to change the logo on the box to fit the new logo of the commercials. I actually think they made a poor choice in style as their PS3 logo is not all that legible now anyways compared to that of the big and clear XBOX360 logo. You could catch the tv for a split second and read the 360 logo where as you see the PS3 logo and it looks like something foreign... Oh fuck me. That made me just realize that's maybe why they did it. Disassociation from being a national company. Plain English makes people think of America or England, where as if it's a stylized logo the association may not be as strong and thus they don't have to worry about that problem in non English speaking regions. I know Sony is a Japanese company and most people do too but I also know that Sony for long has tried very hard to be seen as an international company and not a Japanese company. (that's why their name is Sony, a made up word that exists in no language)
Anyways yeah I think the old logo looks better from an artistic side but the new PS3 logo makes sense and overall I don't think it will have a direct impact on sales but does help the consistency of the image of the company.