In fact, no.
Transparency is always progressive in decent png images (it takes a few pixels going from 255 to 0). And u can't correct that with any built in tool in photoshop etc...
It demands either some time (5 minutes mini for this kind of images) or some smart programming.
Also, the plan in using a "generator" is often to get many many version of it.
@watabou
Consider adding even a SLIGHT LITTLE support for at least background transparency, because i get that supporting the other colors transparency is hard + kinda useless :
PLEASE support the " fill-opacity=" in the custom palettes, even only for background, again !
This don't look like a lot of work, and this would be amazing !
Anyway good work, to say the least, as i really love good artists making bright use of numeric strengths <3