I believe we are balanced in a percentile system. The rebalancing is what people call a "nerf VU."
So the actual number you have in a skill really doesn't matter in the long term, it's your progress vs. the progress of everyone else. In the time between "nerf VUs" we see linear growth in our abilities as the skill numbers grow, but when they reapply the percentile system (once a year, maybe 18 months) we all feel the difference. Some people don't feel a hit, but it's because they have been growing rapidly. Other people get punched in the nuts.
I don't know, it's hard to prove, but that's how I see it.