That really is just a guess; if anyone has evidence that Oprah's a huge bitch on the Internet, I'd love to hear about it.
These people not only believe what you've said, but also they don't think your claim is trivial and won't immediately try to one-up you. But here's the kicker: They don't care. Remember that anonymity thing? You're basically a complete stranger to these people, and it's kind of hard to get worked up about the accomplishments of a complete stranger. In the best case, you're likely to receive polite disinterest in response to your boast; more frequently, you'll get snide replies, mocking you for sharing anything about yourself at all.
But what if you've established a reputation and fixed persona in this community, and actually are speaking with people who know you and believe things you say and care what they are? They're your friends, dammit, they have to care, right? Even then, after all the heavy lifting of making friends, you still shouldn't brag ...
"CHECK OUT MY HUUUUUUUGE ASSSS, BITCHES!"
... but it's not the way we speak to our friends. In fact, if they really are your friends and they catch you bragging, the first thing they should be doing is popping your bubble as violently as they know how. Reminding you of the time when you weren't so good at Gears of War, or the time when you played Gears of War instead of passing your second year of university, or the time you forgot to consume anything but diet Dr. Pepper for 34 hours while playing Gears of War and were checked in to the ER with a rapid heart beat and "imploded kidney syndrome." So there you have it, fools. Regardless of when and where you brag on the Internet, the only possible outcome is disinterest, accusations of lying, petty games of one-upsmanship or stark reminders of your other, larger failings. It's why people who've hung around the Internet for awhile talk very little about themselves and spend most of their time viciously tearing other people down; behavior that is, sadly, the current apex of Internet maturity. ____________________________
For more from Bucholz, check out 5 Silver Linings Now That Identity Theft Ruined Your Life and The 6 Most Overhyped Technologies.