world wide should be your aim if you have internet presence
but it depends on your product/service
sometimes company starts a site just for name sake.
if you are providing designing/coding services and such then worldwide should be your aim.

how marketing is different
well ... locally people who know you come most of the time or people come through recommendation
but sometimes people come just liking your work
the same is the case with internet

the main thing is advertising is more crucial over the internet since there are millions of sites out there and your site has to stand out.