Nickelodeon definitely copied Disney Channel.
Let's face it: both channels are doing extremely well, thanks to the Youtube generation. On Disney Channel, instead of getting family-friendly shows about tales kids can relate to, we now have sitcoms with canned laughing and ridiculous plots (a girl with secret pop life, two twins living in a hotel, a family of wizards, a black dude living in the White House...OH WAIT A SECOND!).
On Nickelodeon, we used to have funny and original cartoons that everyone could enjoy, now not only do we have dull yet easily profitable cartoons (Madagascar, I'm looking at you), we also have more sitcoms with even more canned laughing and ridiculous plots (an average tweenaged girl who's the host of a famous internet show around the world, that girl from Akeelah and the Bee becoming the VP of some fashion line thingamabob, and it's not a sitcom but, a mockumentary about some kid band that seriously, seriously, SERIOUSLY isn't that great).
Well, I should just cut to the chase. Disney Channel has been able to profit so much from one thing: music. High School Musical, Camp Rock, Hannah Montana. 7-year old girls go crazy for these things. Also, have you noticed that pretty much EVERYONE who acts on Disney Channel sings? Even Mitchel Musso sings. Yeah, if Shia LaBeouf was part of this Disney Channel era, he'd be singing his face off, too. All that Disney Channel does it make their actors / actresses be taken more seriously as a celebrity more than they actually are (Does the name Brian Stepanek ring a bell to you? ...I didn't think so.).
Then Nickelodeon thought, "That's easy." So, they invented iCarly, made all of their stars become "superstars", got Miranda Cosgrove to siiiiiiiiiing, and create even more music with shiznit like Spectacular! and many more to come. Proabably. So it's practically a fact that Nickelodeon bases their current success on the success of Disney.
Now if Cartoon Network entered the fray, where do I begin? >_<