There are over 6.5 Billion* people in the world of those people are all connected to one "place. The Internet. That's a pretty powerful email list concept if you really think about it. So why not utilize this power of connectivity to market your business. Targeting an online market, based on location and demographics.
For physical business' marketing to their local community, or an online market, which targets a group of internet users, which have a common interest / goal, where location doesn't matter. Marketing an offline business, online, is harder than marketing an online business, online, because you operate and market from a computer. A business with a physical location is restricted by demographics and will limit the size of its market drastically.
Not necessarily a bad thing, but as the saying goes, the bigger the market the bigger the bucks. So talking about online business marketing... Everyone will be a part of many different online markets. Some search for information on specific topics, some search for things they need buy or for a business opportunity. It can be broken down into many different markets which many people will eventually share in one way. Everyone is connected to each other through people they know, and the people they know, and so on.