Here's a list of 2012 Billboard Hot 100 singles, for reference:
'Sexy and I Know It' - LMFAO
'We Found Love' - Calvin Harris ft. Rihanna
'Set Fire to the Rain' - Adele
'Stronger (What Doesn't Kill You)' - Kelly Clarkson
'Part of Me' - Katy Perry
'We are Young' - Fun ft. Janelle Monae
'Somebody That I Used to Know' - Gotye ft. Kimbra
All of these have an inherent listenability to them. And yes, listenability isn't really a word, but it should be, dammit. They're all easy to listen to, follow a set musical formula with little-to-no deviation. The first four have already established fanbases, but the last two are interesting in having driven up interest through other means -
Glee and commercials for Fun, and YouTube for Gotye. Like the movie industry, it appears that 'hit' music is becoming more and more established on known-properties that either have a lot of success already behind them directly or indirectly. And then of course there's the radio, and the fact that people who buy singles are more likely to base their decisions on what they keep hearing on the radio, as opposed to reading album reviews or generally stepping out of their comfort zones. 'Cause if more album-buyers bought singles, the charts would look very different indeed.
^I have to agree on this for most part. The songs in the Top 40, especially whatever's number one, are easy to listen. They have catchy and dancey beats with just as catchy lyrics (usually overly sexualized and have no meaning) that people can easily sing along too. Although I listen to any of the above songs alot except "We Are Young" , they all get tons of airplay. There's also a ton commercialism involved. I'm a fan of fun. myself,even before their major popularity, and their first album was released in 2009. Although it had tons of positive reviews, it didn't receive as much attention as their current album Some Nights. This is obviously because Some Nights has 'We Are Young" on it and the song only gain popularity due to Glee's cover and commercial use. Another example would be Neon Tree's "Animal". The song gained tons of popularity when it was the Free download of the week on Tap Tap Revenge 3. Owl City, one of my favorite artists, is another prime example. His song "Fireflies" was The Free Single of The Week on iTunes and weeks laters was number one on the charts. Though Adam Young, or Owl City already had a pretty big fanbase, he didn't gain massive popularity until "Fireflies" hit number 1.
The producers are also a big part of it. Dr. Luke, for example, is one of the most famous producers who helped mad people like Katy Perry and Ke$ha popular. Dr. Luke has produced and co=produced many of the number ones that are on the charts today and number ones in the last 5 years. A good majority of songs in the top 40 today were produced by him. Get any famous producer or songwriter together and you have a #1 hit.
Lastly, good looks help alot. It seems that the people with sex appeal or is "hot" or "cute" are the ones making today's hits. And most of the popular artists only have the good-looking appearance and not much or little actual talent.