It's possible to be more valuable to another company. I had a developer ask me for more money and I was just honest, if he likes working here he can stay because he was a good developer but he would undoubtedly earn more elsewhere. He just wasn't valuable to me because I had to be more involved in is projects, going to meetings with him for example. He was a great developer, but the climate of my company was a smaller company with strong personalities at the mid-level for the groups we worked with, if you weren't confident you got destroyed. He ended up getting a much higher offer, tried negotiating a small raise (especially compared to his offer, he still would have been at least 30% below that offer) and he just literally was not worth another penny to me but I know he's doing really well at his new company.