Tobias Buckell said on Twitter the other day: "What is with older folks in the Midwest adding a definite article before a product term? She's not using 'The Facebook' it's just 'facebook.'" This prompted me to begin wondering seriously about why this is so.
The inestimable Language Log addressed George W. Bush's infamous use of "the Google" a couple of years ago, but I have a theory.
We use "the" to refer to items that are unique in their context -- items where there's only one of them that we could possibly be referring to. We say that something fell on "the floor," even though each room has its own floor, because in any given room there's only one floor. For this reason, "the" is used when referring to monopoly public services like "the phone," "the water," "the electricity" ("oh no, the electricity went out"), "the newspaper," "the bus," and "the train." ("The hospital" is a special case; there may be many hospitals, but when you use "the hospital" you're referring to the generic service of hospitalization.) But nobody says they came by "the airplane," because we're keenly aware of air travel as a system of competing providers.
People who talk about "Google," "Facebook," and "email" without using "the" are aware of them as entities in a system of competing providers. ("Email" doesn't get a "the" because it's one of many communication alternatives including Twitter, IM, and SMS.) We look something up "on Google" because we are aware we could also be using Yahoo or Bing. But older folks who are familiar with public utilities but new to the Internet (note: "the" Internet because there's only one) have probably just been handed the one search engine by whoever configured their browser, so they treat it as something like a public utility -- they look things up on "the Google." Likewise, they are unaware of social networks other than "the Facebook" or communication methods other than "the email." You can expect to see this usage for anything that becomes dominant enough that the speaker is unaware of alternatives.
That's my theory and it belongs to me. And it's mine.