The ps3 is expensive if it holds no value to you. Generally people decide if an item is to expensive based on its worth to them. If a person is only looking to play games for fun at low cost the wii is there best option, but if they want high end console graphics they need to choose between the ps3 and 360. If the buyer is living on a budget with possibly no HDTV and does not care about the HD formats the 360 is a better choice because of its cheaper price and equal quality of games to the ps3.
For example I could go to my local BX and buy their Military appreciation 360 value pack for $450 which includes the premium console package, X-box Live Unplugged, Kameo, Viva Pinata, Project Gotham Racing 3, and year membership to X-box Live. Or I could go buy a ps3 for $600 which comes with no games or even HD cables. Even most department stores are bundling premium 360's with a game. This is one example of why the ps3 is too expensive to me because even though I own a 50" inch HDTV I don't care about HD or Blu-Ray formats I just want a great gaming console for the best value and to me those were the Wii and 360which costs $50 less for both than the ps3.
Which console has the greatest games is normally the biggest factor in which console is most succesful. PS3 still has some great exclusives but they have lost some big titles and most third party developers are going multi console which is great for gamers but hard on ps3. They are also competing against two consoles that have huge user bases at the moment but as anaylsts have said the ps3 is selling a little bit better than the 360 initially did when it launched but time and sales will ultimately prove if the predictions of the ps3 eventually surpassing the wii and 360 will come true. In my opinion Sony will still be hugely succesful but I think the 360 will be the more dominant high end next gen system but as long as the wii keeps up with demand and gets better games it will be the biggest seller.