It's designed as a safety net for people who can't find a decent job after taking out student loans.

If you get a high paying job you're not going to qualify for the income based repayment plan because you only qualify for the newer income based repayment plans if it will lower your monthly payments below the standard repayment plan.

Yes, and also there's lots of non-typical deductions that can furthur reduce your effective income for these plans, and ways to reduce the forgiveness period to 10 years. Lots of lawmakers say that program is not sustainable, and Congress may try to change it soon... If your not utilizing it and have student loan debt, I'd recommend looking into it sooner than later, as you may be grandfathered in if/when it's restructured. Most people who are elegible don't take advantage of it yet, and loan servicers do their best to steer students away from signing up for IDR.