Actually, they're not. Since they submitted their patents into a standards body to be used in promulgating standards, and since the standards body requires it, they must demand fair, reasonable, and non-discriminatory rates. This is not "whatever Nokia want."
You're assuming all the patents in contention are standards. Nokia holds a lot of patents around cell phones. They could include GSM patents, interface patents, even touch screen patents themselves.
I know it's hard to believe, but cell phones and even touch screens existed before the iPhone was even a glimmer in Steve Job's eye.