That's pretty much what happens with all consoles. They stick their foot in the water for a year or so and then dive in. For instance, the PS2 was dragged-on for quite a while while the PS3 was being actively used. And notice how both Sony and Microsoft have many other products besides consoles, where as computer companies have the luxury of focusing on computers.
Yes you are right, developers continued development on the PS2, however PS3 games were built from the ground up for the PS3.
Resistance, Uncharted, Madden etc were not PS2 games unconverted on the for the PS3. They were built for the PS3. While games like built for PS2 continued to wow PS2 gamers, they did not hinder PS3 development.
For instance.
Crysis 2, looks great on every single platform. And it takes advantage of every platforms strengths. It will look amazing on the 360, yet even more amazing still on the PC.
Deus Ex 2. A game that was SEVERELY downgraded in both graphics and gameplay depth so it could launch on Xbox as well. Modders then had to work extensively on it for years, and still never got the game up to snuff.
GUN is a game made for PS2/XBOX, released for next gen, praised for gameplay, but the graphics hindered its reception, it did not live up to its potential.
Developing for the lowest common denominator is sometimes easier on developers, but it is ALWAYS bad for us gamers.
And I value gamplay over all else, as I still play DOS games on a regular basis. However, to deny that better graphics and more immersion are bad? That is nonsensical.