IMO, with a fixed # of spots, the inclusion criteria should be more objective and applied strictly.
The problem in this case is not everyone has equal access to a cabinet.
There's a lot that lies within the word cabinet...
Richie is the definition of an arcade cabinet collector/hobbyist. He takes the time to find old machines, transport them, strip them down, sand them, repaint them, rewire them, replace electrical components, install a new (old) monitor, buy new buttons, fix the control stick...etc. There's a bit of extra time/effort that goes into being able to play a game on a real arcade cabinet...sometimes a LOT of extra effort/time. Not to mention the cost of purchasing these machines...nor the fact that you can spend months sometimes trying to find one...and still come up empty handed...which as Hank pointed out, is also kinda part of the problem for people that can't locate a cabinet to play on.
For MAME, you download a rom in half a second, for free, and you're up and playing on any home computer. Quite the shortcut...
And I don't mean to be Policeman Paul or Carl the Cop or anything, but unless you actually own an arcade cabinet...isn't playing DK on MAME technically illegal? I don't see anyone from Nintendo joining forces with Lars Ulrich to come after you anytime soon, though...
The KO is an arcade competition, and MAME emulates arcade games. If Twin Galaxies goes through all the trouble of getting 20 DK machines up and running...what would be the point of all that time/effort/cost if they allowed MAME scores? (during KO1 and KO2 they actually needed MAME scores to fill up a top 10-12, but that isn't the case anymore)
What if Twin Galaxies said, this is too hard, forget the cabinets, let's just get a bunch of computers and setup 20 MAME stations. What would the arcade people do? A few would probably be pretty bad at using a keyboard...and how would that make Twin Galaxies look?
"Uh, so this is the Kong Off, the Donkey Kong arcade game competition...uhh, where are all the arcade games then...and what's with all the laptops?"
Does the answer lie somewhere in between? Should they setup a MAME station for the MAME players that breach the top 12...and let them play on their own MAME computer all day? I can already see what someone on an arcade machine would say about that..."hey that's unfair because this is timed and they can restart much faster than I can...", "hey using a keyboard is easier because you can change directions faster...", "hey they get to sit in a comfy computer chair while I have to stand up, or sit on this hard-as-a-rock wooden stool...".
Or, should all the points above be thrown out because it's not about arcade machines at all...this is simply about skill at the arcade version of the game Donkey Kong. There are good arguments on both sides.
I don't know what the fair/right answer is...but I guess this is all moot because seems the decision has already been made. Interesting points of discussion, though.