Typing appears very, very slowly on some webpages

I was just about to post that when I use safari, typing into webpage text boxes comes up very, very slowly - I'm not a particularly fast typer, but I can finish typing a sentence before the first word appears on the screen on many websites.

However, I'm noticing that this problem does not exist here at the Apple website.

Could this be a Safari problem, or is it likely a problem with the webpage where I'm posting? It seems to happen on many message boards.