It's new roads in the same fictional Colorado. Same scenery, new places.
I think it's a great set, and the extra rally equipment they've incorporated into the Evo and STI explain their absence from the initial game. I've already bought virtual access to these cars over a dozen times over numerous platforms, and between titles on the same platforms. I can do it again. They may share data, but FH is not FM4, and vice versa.
Would you rather they skip all of these in favor of a set of obscure rally underdogs that FM4 never had? That might be cool, but some of us are happy to have these cars back.