Nehalem is very similar to bulldozer in the way it was made, as you said from the original Pentium. The bulldozer is also made ground up as was Nehalem. Westmere and sandy bridge are additions and improvements on Nehalem "Since its modular in nature".
Bulldozer will be made up in a similar way a new arc. but a base has to be there like Pentium was for the Nehalem, maybe bulldozer will be based on Am386 or K6, both are very good arc's.