I think the main focus for Sony should be to release the PS4 at a lower price to the Nextbox and advertise the hell out of the fact that you can play online for free (Assuming that Microsoft will still continue to charge for it).
I don't know if it's exactly the same as the U.S. But here in the U.K. it seems to be that the Xbox was more succesful because it was the cheaper console to play "next gen" games on. Then when COD took off, the majority where playing on the Xbox, so many others went with the 360 so they could play with their friends. Hence it's become the "trendy" console.
At which point there seemed to be a lot of apathy about the PS3. Because even if they where missing out on exclusives, they were able to play the majority of the games they wanted to play on their XBox and they could play it with all their friends. The impression I get from most people is that "Well the grass may be green on the other side... but it's still green enough here, so why go through the effort of moving".
However once the new consoles come out and people are forced to choose a side again (if they want to play the latest games) then I don't think brand loyalty will win out over price. Especially in the current economic climate. Again this is just based on my impressions I've gathered from the U.K but it sounds like the U.S. could be quite similar.
Edit: This is all under the assumption that the third party's don't support Nintendo again. (If they do then I think things could become a bit more complex).
