In terms of pushing talent, ratings matter when WWE want them to matter. Meaning they'll use it as a reason to push or not push a guy depending on how he fits their criteria and agenda.
Now, having said that, it does seem that ratings matter less and less when it comes to pushing someone. It's probably the fact that 3 hours RAW have a very consistent pattern - 1st hour strong, 2nd hour holds up, 3rd hour it drops - and no matter who you put in what spot, that pattern wont change in any significant degree so they don't even have much room for any bias to affect a push.
Punk got mediocre ratings, Orton gets mediocre ratings, Bryan gets mediocre ratings...shyt, Cena barely moves numbers anymore it seems. So WWE doesn't have much to hold on to anymore.
Business wise, ratings matter only if you are very high or very low IMO. Specially with wrestling because unless you have a monster audience, you wont have much leverage when negotiating TV and endorsement deals.