Apple requires you enter a website when submitting an app. They have rejected apps for using a website unrelated to the app or the developer. Plus, some potential customers check the website, and if it doesn't look "real", might not download/buy your app because of the fishy smell.
So put up at least a one page semi-professional looking web page, with info about the app and the developer. Link from your site to the iTunes page for your app to make it easier for impulse shoppers to buy. Support info and a contact form gives potential customers more warm and fuzzies. Google indexing of your website makes info about your app fill more of their search results. I recommend buying at least a cheap domain to use for both this web site URL and your reverse DNS app Bundle ID. Should be able to do this for only a dozen or so bucks per year.