When the PS2 first launched, Sony demanded that all games on the system be enhanced visually over their rival platform counterparts. The PS2 represented the next generation of gaming, and software was required to support this notion.
With the PS3, Sony seemingly has no such requirements, offering us only that it "expects and encourages publishers working on PS3 titles to take full advantage of the technology and features that PS3 provides." Well, encouraging may not be enough. And promises for better looking games in the future don't really cut it. The PS3 is here now, it costs an extra $200 (at minimum), and the visual difference is questionable.