Smartphones and other web enabled phones are different though. There are a number of people in the US that don't have a land line or even cable TV, so getting basic internet service is next to impossible without adding bundled services. If you've never owned a PC before, you then have the hurdle of just getting familiar with what is available and what will meet your needs.
Cell phones don't have that hurdle. Many people without internet access already have a cell phone, so it is just a matter of upgrading that to a device capable of browsing the web and adding some internet plan to your account. From there, you can access popular services like Facebook and Twitter. In fact, I've noticed some of these services allow you to create an account right from your phone, so you could sign up, log in and have dozens of friends by the end of the day without ever touching a computer.
You can read more about the report at CIO Today which gives statistics by minority group compared to whites. Whatever the driving factor, the more people that have access to the internet and have the knowledge to use it, the better.