1 It's 2003 JC Staff.  It's very possible it was rendered to some form of higher scale digital film stock.  Somewhere around 576p or so, so the upscale really just needs some smoothing.  It really just depends on what mastered it to.

There are actually some older series, like Card Captor Sakura, that was rendered to 35mm.  No one seems to know why, but it does look very good.

Though a lot of that stuff, especially the Gonzo stuff from that era, that was mastered at slightly below DVD quality in the first place.  That makes for those horrible upscales.

2 Really, doesn't everything need a bit of Ikkitousen?

3 If, in fact, it was originally done all-digital, and if it was properly archived, it wouldn't have been all that hard to go back and re-render it to a larger size.