Digging the Sweat Stuff

I love sweat.  I mean, except for when it drips into my eyes and burns like the devil, of course.  But to finish training and actually be dirty...It's kinda delicious, isn't it?

I wonder though why we guage our effort on something so easily manipulated.  If the environment is hot enough, you'll sweat regardless.  And if the ventilation and cooling is good, you may sweat a little less.  Does that change how hard you worked?  If the person who crosses the finish line next to you is dripping while you're lightly misted, did they run a better race?  Does no sweat angel equal a sub par performance?