I'm never actively looking for a new job but my resume is always up to date and I never turn down a recruiter who approaches me with a possibly interesting position.
I've increased my salary by over 100% in the last 5 years but have only changed companies once in that time. I've almost tripled my salary in the past 8, also with only one job change. Some of that was leverage after another company made me an offer I could not ignore and my current company wanted to keep me so they bumped my pay. Twice I've simply asked for large raises based on my performance, responsibilities, work load and merits of my own work. I simply stated my case and the company agreed. One of those requested raises was for $25k more, which they ponied up for.
You don't HAVE to switch companies to get more money, I just think most people are more comfortable asking for more money from a company they have no ties to because they have some strange feeling of remorse/unloyalty in doing so with their current company.