Until companies start offering the salary that they are expecting to pay for the position in their initial offer, you're always going to have to ask for more to get it.

There are a few startups (Buffer or maybe Zapier?) that are doing this. Offers are very one-sided, the company has all of the information and you have none. By not negotiating a better offer, you're leaving money on the table. It doesn't help that there's a taboo in our society around negotiation and bargaining.