If you have business cards, you should have a web page. Think of it as incredibly low-cost advertising for your business, your service, or even just thoughts you want to share with people. That's when you really start building a relationship with your customers.
Print is portable.
You can carry business cards in your pocket, but not your web site. You don't have to explain to people how to use your brochure, ads, or business cards. You don't need a computer in order to use a business card. Print is portable, low tech, and familiar. The internet will never replace it.