1) Is there evidence in the code that awarding only 500 points is intentional? It seems either the 800 displaying or the 500 awarding is a glitch.
From the commented code posted elsewhere, here's part of the score-awarding stuff for jumping objects:
LD DE,#0001 ; 100 points
LD B,#7B ; sprite for 100
RRA ; is the score set for 100 ?
JP NC,#1E28 ; yes, award points
LD E,#03 ; else set 300 points
LD B,#7D ; sprite for 300
RRA ; is the score set for 300 ?
JP NC,#1E28 ; yes, award points
LD E,#05 ; else set 500 points [bug, should be 800]
LD B,#7F ; sprite for 800
JP #1E28 ; award pointsI think that the commenter is making an assumption here when he says that setting for 500 points is a "bug, should be 800".
The mistake is either the "#05" (the value of the point award - 500) or the "#7F" (the location of the 800 sprite in the sprite table).
IMO, the intention was to award 500 points (as the game does), and the sprite location the code means to reference is #7E, which is the 500 sprite, but it mistakenly references #7F, the 800.
Why do I think it's meant to be 500? Because the progression just makes more logical sense - 100 for a single, 200 points more (300) for a double, and 200 points more than that (500) for a triple.
It also just seems that a human putting this code together would be more likely to reference the wrong sprite than he would be to directly type in the wrong value ("5" instead of "8"). Wrong sprite would just be an easier mistake to make.
The code above calls #7B, #7D, and #7F respectively, for 100, 300, 800.
Since 7D is 2 up from 7B, and 7F is 2 up from 7D, he might have been thinking in "200 points between each award, so two sprite-locations between each award" terms. The error of course is that there's no 400 point sprite. Interestingly though, there IS a never-used "200" sprite at #7C. You can see that yourself by running the game in MAME, hitting F4, hitting Enter, and then the "]" key. There you can see the mysterious 200 sprite. Check out #4C as well. That falling pie sprite (which is never used in the game) was actually the initial seed of inspiration for Jeff Kulczycki to make D2K.
What I find most interesting of all though is that, even through 5 total versions of the game (3 Japan, 2 US), released over the course of more than half a year from first to last, this bug was never caught.
2) Although probably less frequent of an occurrence, does the same happen on the pie factory?
Only the barrel board offers a "multiple jumped objects" award. On the other boards, if you jump and there's an object in the "scan area", you get 100 points and that's it. It doesn't matter if there's more than one. Point pressing on the other boards would actually be way more complex if you could do combo-leeching...