I take my coffee seriously and I'm willing to spend some time (and money) making it. Even for me, that looks a bit more involved than I'd like.
Or if you accidentally put the plunger in the wrong side and don't notice before you fill it up. I did that once :)
Motion seconded. I used to think inverted seemed complicated as well, but once you've done it, it's pretty darn straightforward.
Still, I hesitate to recommend it to some people, not because it's difficult, but because I know they might use boiling hot water straight from the kettle and risk injury. Under the right conditions, it can separate when screwing on the filter cap, due to the steam pressure.