There are a lot of variables, too.
Are you loading 1 text page every 5 minutes and then just reading it slowly? Or are you loading new image-heavy pages every 30 seconds?
And are you near a tower with 5 bars of 3G and a fast connection? Or are you waiting for a slow, 2-bar connection to download stuff? Not only does it take longer, I've found the phone has to work harder to maintain the connection.
So the short answer is: "that's normal." But the long answer is: "if you'd been at 85% or 95% I'd call both of those normal too."