I believe boot chess also does not implement two of those three, which makes it a fine comparison. Promotion is something I expect most people know, castling is something they might know, but en passant is hardly common. I wouldn't be at all surprised if the number of people who play chess without knowing that rule exceed those who play by FIDE rules.

Whatever the case, it is still a variant of chess, so I see no problem calling it chess.

Promotion shouldn't be compared to castling/en-passant here.

A game without castling or en passant would be similar enough in spirit that we could call it a "chess variant". Removing promotion, on the other hand, would result in a wildly different game.

I actually suspect it'd be impossible to win against any non-beginners, making it more similar to tic-tac-toe than to chess.

En passant comes up a lot more often when you don't know the rule.

But ... that's like moaning that Bannister broke the four minute mile but collapsed at the finish line.

1K is a hellava achievement

It would be more like moaning that he broke the four minute mile but collapsed fifty feet before the finish line. Should it be counted if you didn’t finish?

This program is awesome, but it’s not quite chess.

Nonsense. Bannister ran a mile. I've made lots of programs that were under 1K. They weren't chess, either.

I don't like how negative this comment is, but the logic is flawless. I have also made a lot of "<1K not-chess" games.