As far as we can see, there's truth to be had on both sides of the fence. However, we do have one point of contention to make with Grimwelll's argument. He states that the reason fantasy "pwns" sci-fi is that it's accessible, which is a constant argument on the matter. While we think he may have a point in that less people are inherently familiar with sci-fi, we very much disagree with his assessment that you need to be a math nerd to enjoy good sci-fi -- his example in this case being Star Trek and its now-infamous technobabble.
We would like to point out that many of us here at Massively enjoy sci-fi quite a bit and few-to-none of us are anything close to math nerds. There's a lot more variety to the sci-fi genre than what Grimwell seems to take into account here with Star Wars and Star Trek. Examples are Battlestar Galactica, Babylon 5, Dune, Doctor Who, Firefly/Serenity and many others from books and videogames alike.
He continues on this approach, saying you have to be properly educated to suspend your disbelief in any sort of sci-fi. This doesn't ring very true to us considering that many children have been taken in by shows with characters like Captain Kirk or Flash Gordon over the years. If sci-fi required you to be a math nerd or a college-grad then why in the hell do so many people watch these shows? People are constantly enjoying shows like Heroes, Lost or The 4400 when they're so obviously not fantasy, but sci-fi.
We think that It is the quality and content of television shows, movies, books or videogames that make them compelling, rather than whether or not it's fantasy or sci-fi.