Wow OP, you have no idea how modding and the mod community works, do you? Nor, apparently, do you know how game development works - but most gamers don't, so I guess that's to be expected.
Modders ALWAYS create things that a game dev has not yet created, and oftentimes they're better than what the devs create. In this case, it's sheer numbers - Mojang is a 6-man team. How many modders are there for Minecraft? How many modders are working on bug fixes, prototyping/creating TWO new games, implementing features like the "adventure update" for 1.8, AND planning future updates as well? How many modders have to worry about making sure their mods work correctly in both single-player AND multi-player?
Answer? None. Modders are lucky because they only have to focus on what their mod does and make it work successfully with the game. That's it. They don't have to look at the game as a whole, don't have to worry about how it's going to work with features in 1.8 or 1.9 or 1.10 or any other subsequent update. They don't have to design and program other games outside the parameters of their own little mod, and they also don't have to deal with anywhere near as much fallout should their mod fail. The most a modder has to do once their mod is released is make sure it works with subsequent patches. Hell, they don't even have to do that - it's completely voluntary.
You're also forgetting that not everyone mods their game. I'd wager that most people who have Minecraft never go on the forums and never bother to keep up with what Mojang is doing. So before saying that Notch adding in pistons is "useless" maybe consider that not everyone is you and doesn't have that particular mod. So for the, oh, over one million people that don't have that mod, pistons are going to be of great use. They're also going to be automatically updated from now on with every subsequent patch so you don't need to worry about the modder fixing his mod every time Minecraft gets an update.
That's one thing many gamers forget - the vast majority of people who play games are not online discussing them. They're not going to bother going to the website beyond getting their game, they're not going to look into modding and mod downloads, and they're not going to keep up-to-date with the product that they're playing. They're just going to play the game and check it out occasionally when it gets a new update. That' it.
Goodness, it's things like this that's made me absolutely fed up with the Minecraft community. Throughout all the sites I've seen them on (various gaming forums, Minecraft forums, and especially YouTube) I don't know if I've ever seen a more petulant and whiny crowd.
And really? Dismissing everyone who disagrees with you and saying they're just "pooh-poohing" a good point? Huh. I guess it never occurred to you that your opinion is subjective, did it? Nor did it occur to you that making a post that's a game dev is not going to make people inclined to agree with you. Well, good luck with that. If you're getting laughs from some of the posts, then good for you, because I suspect that's all that this thread is going to be good for.