Great comments DJ quad. You are right on the money with what you said about variety. With regards to repetition, sadly from what I've observed and read, some of the most successful stations of alltime were very heavy on the repetition.
To NoMoreLurking, if you have 4 Rock stations in a market then filling a niche is fine, but if you just have one then it needs to have as broad of an appeal as possible.
If there were 4 stations in NYC leaning on Dance then you'd expect one to go full blown Dance.
While NYC already has 2 Hip Hop stations this did not happen overnight. NYC does not have a true Rhythmic CHR (although KTU and 92.3 Now straddle that line) nor a true Dance station. In order to create a Dance station for NYC you first need to create a mass appeal station that's going to cater to more than just the Dance heads. Mass appeal indicates it needs to be Pop savvy, and since a lot of Hip Hop records are also big Pop hits then it makes sense to play some Hip Hop in the mix.
If there will come a time when there will be a big enough hole in the market for a pure Dance station in NYC then you'd likely see it emerge on a full market signal. You'd see signs of this emerging if the Pop charts were suddenly flooded by Dance records, as was the case in the late 70s with Disco.
We've brought up cases of the original Hot 103, which debuted in Summer 1986. A little less than 10 years later, in the winter of 1996, New York got another Dance station on the same frequency, 103.5 KTU. The new KTU wasn't pure Dance, but was a VERY smart mass appeal station. It played Dance, Pop hits as NYC didn't have a true CHR/Pop at the time (Z-100 leaned Modern Rock), and it played retro Dance, including titles from the 70s and early 80s that were popular on the original 92 KTU. Hence, it was a very different station from both the original Hot 103, and from the original 92 KTU, but it was mass appeal.
With regards to Rock, the Rock audience in the major markets has gotten increasingly fragmented over the years. Some of the Rock fans are anti-radio, some only want to hear a very specific type of Hard Rock, Adult Rock, or Alternative Rock. Concurrently, the major markets have gotten a lot more ethnically diverse over the years. Rock radio, like Country music, is at its core a format big with white people. And yet, Rock music was created by blacks, and has been embraced by Hispanics a lot moreso than Country music.
Rock music is associated with the baby boom generation. It was the voice of the young people, and in the post World War II era teens accounted for a much higher percentage of the US population. Many of the Top 40 stations in its Golden era were geared at 12-24 year olds, and thrived thanks to the music coming out of Memphis, L.A., Liverpool and Birmingham. Progressive and pure Rock radio was then able to take off due to Rock's huge popularity. FM radio was much more experimental in the mid 60s through much of the 70s, and was where Rock stations of all shapes and sizes found a home. By the time the 80s rolled around, when radio had gotten more corporate, and many stations couldn't rely on 12-24 year olds to survive, there was a big enough older audience for Rock. That's why many of the Rock stations of the 80s were more Adult friendly, and being a Rock station oftentimes meant playing Bryan Adams, Bruce Springsteen, and other acts that today many Rock fans would frown upon. They want it hard and loud, or they want it melancholic and indie, but they oftentimes don't want something in between, those mass appeal records that bridge the gap between young and old, loud or accoustic. And that's what makes it harder for Rock radio to succeed in some markets these days. So some people stopped listening to Rock altogether and moved on to other genres, and some found new outlets for their music - namely the internet.