What's wrong with realizing a game is boring after 20 minutes? Is there a globally-agreed-upon rule that states a gamer absolutely needs to play a boring game for more than ten hours or an entire week before realizing said boredom kicked in well within the first five minutes? If a game just isn't for you, you'll know really fast. Yes, sometimes there's exceptions, sometimes you might think "damn, this game is bad" right away, but somehow you tell yourself "well... let's... let's just keep trying" and surprisingly, at some point, it boards the "damn, it's actually getting fun now?" sleeper hit wagon. But it's not always like that.
It took me about 30 minutes to stop playing World of WarCraft, never touched it again since then. And, on a side note, Steam Refunds is extremely overdue. It should have been there years ago.
The only thing I wonder about is why would anyone bother posting that on the Internet when they know full well (please don't be naive in public) about what the reactions will be. It's not like you'd actually hope for and expect a detailed pages-long conversation in a thread where only constructive criticism and maturity is the norm, especially after announcing on said forums that you happen to be bored of a game after playing it 20 minutes? It's obvious that kids (and adults with a mental deficit) will be there ASAP contributing with their irrelevance.