First off, Todd Rogers Atari 2600 Galaxian score was what got me into TG in the first place. So I am biased.
2nd off, for Todd it's more for being, "the first professional gamer." Activision did pay Todd to play at events. Given how people are making careers out of it now, it's to pay homage to just that alone. Also I collected for Atari 2600 games at one point. Todd was the first competitive gamer I knew about. It was a hard decision, but I included him in the end.
For Billy it's different. He had five major world records back in the day. None of these scores have been questioned. This is more for 1980s Billy Mitchell than modern day Mitchell. If this was based solely on Billy since 2000 I don't think I put him in.
By the way Bonds and Clemens both got over 50% from the writers last go round. Also, a main argument was that they were Hall of Famers before the cheating.
By the way, the current IVGHoF has both Todd Rogers as Hall of Famers. They don't however have Matt Hall, Dwayne Richard, and Donald Hayes as HoFers. Just food for thought.