Core games don't sell because most of them fall under one or more of these categories.
-gimped port (CoD)
-niche audience (Okami, Madworld)
-bad reviews (The Conduit)
-minuscule budget (Most games)
I can count the number of 3rd party games that don't fall into those categories on one hand.
Lets look at what sells on the HD consoles
-Large Budget (too many to count)
-mainstream franchises (CoD, GTA 4)
All systems have seen moderate success with new IP's (Uncharted, De Blob, Boom Blox, Mass Effect, Bioshock).
I decided to look at all million sellers for PS3 and 360
I came up with...
32 PS3 million sellers
25 are sequels
2 are bundled
The rest are large budget new IP's and are on the bottom of the list.
68 360 million sellers
49 are sequels
at least 3 bundled
several large budget new IP's that are moderately succesfull (most of which under 2 million)
For Wii I get 52 million sellers, most of which are first party, excluding those I see
11 sequels
the rest low budget new IP's.