What you said is totally wrong
HD 3000 series ( RV670) is supposed to compete with G92, G98 and the other G9x processors, not with 9 series
Nvidia don't want to use the 9xxx naming for their new 65nm video cards. They decided to use the 8xxx naming,
And for your information the ATI was going to use HD2xxx naming for their new video cards but they changed there mind and they decided to use HD 3xxx naming
HD3xxx is just HD2xxx with a die shrink and with small changes like adding PCI 2.0 express support.
These changes are similar to the changes between Nvidia G80 and G92
G92 will come earlier than RV670, so this is smart move from nvidia