I'm not sure if this issue is specific to macs, but I'm guessing it is because mac has its own special scrolling features.
Almost every website and app on a mac has a specific feel to its scrolling. You get familiar with it after a while, and your fingers adjust to it so that you feel comfortable scrolling through webpages, apps, etc.
But then once in a while, I come across a website where the scrolling feels totally different. It starts slow, and then suddenly accelerates mid-scroll and doesn't slow down at the rate I'd expect. It's hard to describe what's so jarring about it, but it's really annoying given that any mac user has probably adjusted to the typical mac scrolling mechanics.
Here's an example of what I'm talking about.
Is there a way to disable this, or are we at the mercy of the website designer?