I was thinking the same thing when I first saw the effect Infernal but then after more thought I figured rectangles would probably give worse preformance. A polygon can not bend so a new one has to be created for every time the particle turns and you need several for a smooth curve, that can add up to alot of polygons. Also seeing that the effect is translusent you would see the polygons stack ontop of each other at the joint in the curve and a less-translusent band would show up. I remember the Bid For Power mod team fought with this side effect with the player trails for quite some time and were never able to fix it (they did not have the source but still).
I dont know I just think it would be faster to use a single vertex particle for each bend in the curved line than a costly 4 vertex polygons solution. But I am not a coder so I could be wrong.
I put the new in b!