I think they spent more time developing the Tyrells because the Tyrells stick around more, and frankly they DO play a major part in the series. In the books they're mostly a bunch of Ciphers, and that wouldn't work for the show.
They didn't do anything to "set up" the Boltons more because they wanted to keep it a surprise that they'd turn traitor. It's also why they changed Roose's appearance from the books which would've been like him wearing a "Yeah, I'm evil" sign on him.
As for the lack of warging for Arya and Jon, we already saw warging in Jon's story it just wasn't from him so we know the concept (which is also being shown with Bran). Arya's warging will be saved for season 4 for when she uses Nymeria to do...you know what. It'll be more dramatic that way.
And honestly, there wasn't THAT much time wasted on Ros or Podrick. Folks need to get over how there are some new characters.
PS: I like how they made Cersei and Tywin more 3-Dimensional, compared to the 1-D caricatures they are in the books (which would've been a waste of Lena Headey and Charles Dance).