Yeah, because Nickelodeon brought the property just to kiddify it all up and make it completely unrecognizable to audiences.
Please.
Nickelodeon knows perfectly well what they're picking up, a popular, valuable action-adventure property known throughout the world. If anything, they're picking up insurance when Disney does take away the Marvel-owned properties from the network around 2011 or so. And considering they own the property outright, including the rights the 4Kids-produced series, the series might actually air on the Nick outlets, especially Nicktoons. They're also the ones producing and distributing the live-action film that's about to be in production as well as a new series coming to Nickelodeon a little after the new film is released. This is the same company that gave us Avatar, in case you forgot. They also own TeenNick as well.
Then you hear comments like this: "I hope Nick doesn't turn TMNT into a kiddie franchise." Well, guess what? TMNT is largely seen as a kiddie franchise in this country and around the world, which is why the series doesn't air on FX or Syfy, but rather 4Kids. It's a bellwether brand, something that has spread across three decades in some form or another, and it's a property Nickelodeon can and will manage successfully.
The Turtles will be alright.