This is exactly right. My maths teacher, who has been teaching maths for many many years, himself says that the tests haven't got easier or the students dumber. Nay, it's just the fact that the curriculum is different now. It adapts.
For example, when he was at school, he was routinely using logarithms at age 11/12 just because it was the simplest way to do operations involving large numbers. We didn't start that til I was 16, but we learnt about other areas of maths a bit more. Geometric, series, etc.
Everyone bangs on about how hard old exams used to be. It's simply not true, the students were just learning different things back then.
I attend a state school, and I consider myself quite gifted. I've had a good education all my life and I've always been creative/interested in all things science/maths. And honestly, after all the work that's gone in, I refuse to believe that I'd be in a majority if I'd lived 50 years ago. It just doesn't make sense; my parents' education's standards just weren't different.