[FUTURE SITE OF QUOTE PYRAMID.]
Well, I didn't mean to criticize your painting(because they do look excellent), as up until now, I havn't actually seen anything of yours. Perhaps it came out wrong. And there's nothing wrong with sweating orks(it was just an experiment...). It was supposed to be more general then just targetted at you, as when I think of large brushes, I think of the tyranid or smurf player who quickly coats with 2 or 3 colours, and dips them, then calls it done; as quite simply, you've got me beat.
As for a needle, consistancy, pressure, flow, and density are of no concern when you're painting a tiny point on to something. I could use my 10/0 brush for that, but it's easier to just poke it with a needle and call it a day. It's easier to maneuver a needle through the bumps and grooves in a character's face then it is to move a brush, since needles are so much smaller.
Not to mention that there's also a comfort level that different people have with different brushes. I do almost all my painting (not including drybrushing or washes, obviously) with a 10/0 because it just feels more comfortable to me. Similarly to how I draw, sure, I could use a .5mm lead, but .7 is just a lot more comfortable for me to work with.
For example, this guy's eyes were done with a needle, while the detail on his lense was done with a brush. They both achieve similar detail, but it was simply easier to use a needle for the eyes then it was to use a brush. Of course, that is, if you can actually make out the eyes.