Uh, I don't think you realize this, but people like other games. They are going to want to blend things together. I can see that you don't want Blockland to blend in with anything else, but a little diversity never hurt an- Oh wait.
Let me rephrase that.
A little diversity with weapons expands your ideas for new weapons. An example of this would be the Grenade Launcher on the incredibly old G36C. I used it a lot, got bored of the same stuffty emmiter explosions, and then it came to me. Why does it have to shoot grenades? Why not knives? Maybe knives that explode, or knives that are on fire! So instead of asking Why?, sometimes you should ask Why not? For me, this is what makes games fun for me. Sticking a big ol' middle finger to logic and ethical-uh-iness.
So your argument in favor of emulating other video games within Blockland is because it's like making a gun that shoots knives?
See the problem with this is that these custom game modes don't really do anything new. Pecon's Boss Battles is basically just the boss fighting minigame from Team Fortress 2 with player-controlled bosses. This mod itself is essentially Minecraft, but in a different engine. Jail RP and CityRPG servers are carbon copies of CityRP on GMod and Jailbreak on Counter-Strike.
There are interesting game modes that take advantages of Blockland's unique abilities, things like Trench Wars or Fort Wars or that one server with the disappearing blocks you have to stand on, or the other one with the floating platforms and the knives and grappling hook. But for every one of these there's 50 different TEAM FORTRESS 2 TDM servers and honestly it's annoying.
I'm not saying people can't like other games, or that they can't draw inspiration from those games, but there's a big difference between "drawing inspiration" and "making Battlefield 3 BUT IT'S IN BLOCKLAND NOW." The former can make really cool interesting things. The latter is just lazy and ultimately makes me just want to play Battlefield 3 instead of Blockland.