Löve, PyGame, JS, Scratch, and Shoes, to name a few. The trouble isn't that you can't write a fun game in a few thousand lines of a high-level language — after all, lots of kids spend plenty of time playing Tetris and Bejeweled and so on, which you can implement in a lot less than a couple thousand lines of code — but rather that a randomly chosen game is unlikely to be accessible this way. There are two obstacles.
First, you can always make the game better by adding more code. In 1979, that wasn't the case, because you could easily make the game too big to fit in memory. So even though you can make a playable, enjoyable game in 50 or 100 lines of code, you can make it noticeably more fun in 1000 lines of code, and marginally better than that in 10 000 lines.
Second, most games, especially casual games, aren't distributed in source-code form at the moment. Seebs had the good fortune to be working on Unix, where people distributed things in source because it was the easiest way to make them runnable on everybody else's Unix system. JS has the same advantage, but with Flash and Win32 and Linux, it's easier for users to run your code if you distribute an inscrutable binary than if you distribute the source code. So that's what game authors do.
First, you can always make the game better by adding more code. In 1979, that wasn't the case, because you could easily make the game too big to fit in memory. So even though you can make a playable, enjoyable game in 50 or 100 lines of code, you can make it noticeably more fun in 1000 lines of code, and marginally better than that in 10 000 lines.
Second, most games, especially casual games, aren't distributed in source-code form at the moment. Seebs had the good fortune to be working on Unix, where people distributed things in source because it was the easiest way to make them runnable on everybody else's Unix system. JS has the same advantage, but with Flash and Win32 and Linux, it's easier for users to run your code if you distribute an inscrutable binary than if you distribute the source code. So that's what game authors do.