It's not about better information, it's about speed of information. You can look at a progress bar and instantly gauge the progress of your task. "10.7/75MB copied" is more precise, but of less intrinsic value--I have to calculate in my head where the halfway point is. To get a percentage in my head out of those numbers is even harder.
Try it. Half of 75 is about 37, so I'm a little under a third of the way to the halfway point. I'll be a quarter done at ~19. Takes about two seconds. Even faster for a computer, of course.
Now do that with a progress bar. You can't. What do you do, hold a piece of paper under the bar and fold it in half? Then guess whether the bar is measuring estimated time to completion, percent of data transferred, or percent of files transferred?
You can ballpark it at a glance, sure. It's obviously under a quarter done. Obviously over a tenth. Is it under a fifth? Maybe. We're just not good at judging those things. And progress animations are deliberately designed to make it even harder.
And don't get me wrong-- it's nice to be able to ballpark it at a glance. It reassures me that it's moving at all. It gives me some idea of how much longer it will take. It makes it seem like it's going faster. That's what I'm saying.
