As Glenn said, the point is not the manual clutch (both button and axis) working better than autoclutch, but the autoclutch being worse than those. With LFS you are provided an automation of the clutch pedal called autoclutch, so you don't have to worry about it. But you are also provided a manual way to use the clutch. It happens that the automatic clutch is slower and has poorer performance than the manual one, so it's just natural that some people will chose manual clutch over automatic.
Now, how can you tell that someone using manual clutch is using a macro or not? Well, there's simply NO way. You might say that analyzing his RAF or whatever. But it can perfectly be the case that the guy masters the technique of pressing two buttons at the same time (which is not difficult at all). That's having no evidence at all.
Before, I was against the macro because I thought its performance was unreachable by humans, but after reading glenn's report on different clutch method's behaviour, now I find it pretty interesting. AC is indeed VERY unrealistic, while pedal/button/macro are all more realistic. I don't consider it an unfair advantage anymore, but I consider AC a disadvantage now.