At first I thought this sounded like something ImageMagick could do as well, but after poking around a bit I saw where people have had trouble with this particular conversion in ImageMagick. The suggested work-around is often to just to use Inkscape instead.
The conversion worked well for most of the images, but after looking through more of them, I saw that there was a problem with a few of them, even when opening them in Inkscape’s GUI. I’m not sure why it wasn’t rendering them correctly. Firefox and KolourPaint were rendering them. I wonder if the SVG images were using an SVG tag or feature that isn’t supported in Inkscape.
Edit: I don’t see anything unusual in the SVG source (the values were removed below to reduce the amount of text).