There is not a single element of the game that could be removed without changing the whole thing.
[...] it was already perfect the first time around.
Variable release rate, concocted percentages, and, depending on design goals, time limits. None of these have come to the writer's mind, who argued that L1 is all about small characters interacting with landscape.
I read that statement as an obvious poetic exaggeration to make a point. Even if one ignores the usual things Simon like to rant on, just the levels themselves people have had many likes and dislikes, as evident in the level review threads. A more interesting point may be something like Simon's suggestion of culling floaters as mentioned previously on IRC. That would be a somewhat bigger and thus more interesting removal of game element.
We enjoy a luxury: L1 comes short mostly in usability, which is expected for a 1991 game, 25 years behind modern theory.
It's a little like judging the usability of PC OS's at the time (eg. DOS and other command-line-based interfaces) compare to modern OS's like Windows or iOS. It would be astounding if you can find no shortcomings compared to modern standards. Certainly at the time it hadn't hindered the apparent meteoric rise in sales.
It's interesting how triggered traps are so central to the design.
I feel like it's more related to the history of how the concept came about. Basically the animations was the spark of inspiration, the rest sort of came later. When you started off with all these funny animations already made, and they inspired the rest of the game in the first place, it only makes sense to try to use them as much as you can.
And from my limited and admittedly amateurish experience with creating levels, slapping in yet another hazard is often an effective way to remove a backroute.
I imagine it's somewhat like what they quoted Mike Dailly saying, that the traps were there to "guide" the players so that levels don't become too "dreadfully dull".
It is also probably good for marketing to show off the lemmings getting killed and maimed in hilarious ways.