An article in Deliver: A Magazine for Marketers illustrates the impact of direct mail vs the Internet. While both can be used together for maximum results, relying solely on the Internet can can have a negative impact on the reach of your message.
"Just about everyone has a mailbox, and surveys show that, even in today's online world, people rate 'getting the mail' as a favorite on their list of daily activities. People collect their mail on purpose and at a time of their own choosing. So unlike online messages, direct mail doesn't get in the way of other things they were intent on doing. Moreover, when direct mail is well targeted and well executed, recipients willingly set distractions aside to read. Since that's not something they can do while texting or playing a guitar, direct mail gives you their full attention."