I've countered with more than 50%, and ended up at 50% over the initial offer, though in general I agree with you. 50% up on advertised range or on what the recruiter indicates their range is, on the other hand is far easier. The top end of their stated range is lower than what they're prepared to stretch to.

When I joined Yahoo a decade ago, for example, I ended up accepting an offer 40% over the top of the advertised range, after demanding more. When they gave me the 40% offer, they apologised that they really couldn't go higher (it'd push me too far up over some other people in the department) and offered me more options instead, and guaranteed me a review after 6 months instead of 12 to bump me up further (which they did).

I've never taken a job at only 5%-10% above initial offer, and don't think I ever will - I know from my own hiring that we're always prepared to stretch more than that if we've first decided on a candidate.