For many national or regional chain stores, providing dealer-locator services with robust maps, driving directions and proximity search capability is outside of their core competencies, and they frequently choose to outsource that development work or purchase software to enable the service easily.
I did a quick survey and found a number of companies providing dealer locator or store finder functionality:
Zenoweb Locator 
ZipMath Software 
Some of these services are relatively simple applications using the APIs provided by the big mapping vendors while others have custom-built their applications from the ground up.
As far as I can tell, none of these services or software solutions have built their applications to be search engine friendly as I described in my article on SEO for Store Locators . It’s not all that hard to build web applications to be optimal, but it does require that application developers understand the need and modify the format of their applications to satisfy the additional criteria, and it requires someone who’s familiar with search optimization to specify the needed changes.
Considering the amount of competition among store locator providers, perhaps some will now choose to better differentiate themselves from the crowd by re-engineering their applications to allow search engine spiders to crawl through their content and index their pages.
And, any major corporation should turn to their service providers and insist that they adjust their applications to facilitate local search optimization.
UPDATE 1/8/2008: We have now begun providing local search optimization through our GravityStream product. Check out the details: GravityStream Optimizes Store Locator Pages .