This past television season has had several shows that were very similar, falling into a few themes. For example, The Ringer and The Lying Game both involve a down-and-out female taking the place of her affluent identical twin, investigating a mystery involving secrets and murder, and finding that the new family likes them much more than their twin. In fact, these two shows are ridiculously similar, the difference being that The Ringer is orders of magnitude better. Another new show this season falls in the same theme. Switched at Birth while not about twins, is about a couple of girls who switch (to some degree) families after finding out that they were, well, switched at birth.
Another theme this season has been oldies. Trying to follow in the shoes of Mad Men (for some reason), there have been several shows that take place in the past this season. There was the short-lived Playboy Club, the more successful Pan Am, and the Canadian (and older-set) Bomb Girls.
A third theme this season was that of fantasy. Both Once Upon a Time and Grimm are about fairy-tales in real-life.
Not surprisingly the whole vampire-werewolf-etc. fad continued its presence on television with the release of The Secret Circle and a TV adaptation of Teen Wolf.
I don’t know if it is just coincidence or studios trying to cash in on fads while they can (the way that they all release low-budget movies that have the same theme as a current blockbuster). Either way, this season was very theme-heavy compared to usual.