Seriously though, ive seen mander posting here for over a year and never seen him post a pic. Or anything he came up with. He might just be a me, has a decent understanding of how to implement and improve on existing creations, a decent builder, not truly innovative. Plenty of people like that on this board.
I do have to say though that this board does have one of the best groups of regulars out there. One of the reasons i always come back, even if i do always announce my return with a couple of troll topics, normally ignored at first by the old regulars, till even they get annoyed.
You know, Solnot, it's rare to see you outside of the Xbox 360 board... so, "Hi! How are you doing?".
To address your question, the main reason this game is as popular as it is, stems from a few factors...
First, you have people who start playing this game because of the "word of mouth" effect. A friend starts playing the game, and then starts telling their friends about the game. This is how it starts. Not all of your friends will end up wanting to stick to the game (I was inducted by a friend, who absolutely loved Minecraft, and wanted to share it with me). If even a handful of your friends start playing the game, because of you, they'll stick around (even if they don't exactly love it, too), just because it's a game to have in common.
Which leads on to the next factor... this is a game that can be increasingly funner for a group of friends. Playing the game "solo" can be "boring" for many people. But when you start playing with other people, especially your friends, you start collaborating on projects, and contributing ideas, and seeing how it all pans out.
But, you might ask, what about "solo players"? As someone who is ~very much~ into solo playing, I can say this is a game that, for casual gamers, might not be very fun... but if you're able to unleash your creativity, this is a great sandbox game. There is a little something for everyone. You can construct buildings, you can design inventions (with Redstone), and you can make art.
So... yeah... those are the primary factors for people enjoying the game. I wouldn't say this game is "only for the smart people" or that it "weeds out the witless"... because I've come across quite a few people who aren't very bright at all, who absolutely love this game. But it is definitely a game for people who can express their creativity.
And in a world, where more and more, we're seeing games that are just "Point a retical at a mob, and pull the Right-Trigger to kill it", a game like Minecraft turns into a real gem. It's no wonder, to me, at least, that it's become such a popular game, and has sold millions of copies.
The fact that it starts out as a simple: "Break a block, repurpose it for something else..." type of game, and can turn into an extremely complex system of builds (such as the people who have made fully functional computers, and "games", and those who have made RPG Adventure maps), just further proves that Minecraft is a game that will reward you based on your level of inventiveness, creativity, and effort. If you put in only a little effort, you'll be stuck with Dirt huts. If you put in a great deal of effort, you'll end up recreating Westeros and The Wall.
Hey, don't laugh too hard. My first time on a hard survival world, I had to dig a few blocks deep into the side of a hill (with my bare hands), and hide away (I even blocked the entrance with Dirt blocks), because it became night far too soon for me to even start collecting supplies like Wood, or Stone.
I ended up hollowing it out a bit, created a Furnace and Crafting Table, and then started working on making it "cozy", until I could start making something more... aesthetically pleasing.