This series should be merged with http://www.speedrun.com/mario_kart . It doesn't make sense to exclude this one game from the Mario Kart series.

I think they chose to have it as its own series because there are 2 other Mario Kart Arcade games. I'm going to look at adding Mario Kart Arcade GP 2 soon. I don't have access to Mario Kart Arcade GP DX myself but that should get added at some point as more runs are completed on it.