You gotta factor Revolution into this too. Let's say Revolution launches in between X-BOX 360 & PS3. At first, dirrectly, X-BOX 360 & Revolution will be competing for the next-generation buyers...in fact, they may be so busy competing with each other that they both stumble over each other (like they did this generation) giving Sony time to plan and strike accordingly.
I don't believe Sony would wait 'til 2007 (except, maybe Europe), the longest they'll wait is 'til Holiday's 2006 in the U.S. market.
However, let's say Revolution launches after PS3 (seperating itself from the competition), thus having X-BOX 360 on the market by itself for a much longer period...this would force Sony to counter sooner rather than later 'cos instead of next generation buyers having 2 choices, they'll instead only have 1 (X-BOX 360). Not giving Sony as much time to plan & wait gives them less time for: launch software, launch shortages, to lower costs, to beef up final specs. This also keeps Sony from implimenting any of Revolution's ideas into a delayed PS3. Nintendo can use the higher demand of the other 2 consoles to their advantage giving them time for a more strategic worldwide launch or even capitalize on PS3 shortages soon after it launches.
Hopefully Nintendo Revolution launches as close to or as soon after PS3 and sometimes before the end of 2006.