It seems like satire because the story isn't, even on the surface, about the need for signs in subway stations. It's about a dedicated employee who, performing what many would consider a menial job, displayed care and dedication to his job and in the process revealed himself as something of a design savant.
Saying "but you can print signs for $50" is so wilfully blind to what makes this story charming that it seems like a parody of the literalness and complete lack of romance that one sometimes sees in HN comments.
The Dropbox comment was about a startup making cross platform desktop/mobile sync easy, and a facile dismissal about being able to hack something similar together with FOSS tools which missed both the complexity of the domain and the main point which was convenience for the average Joe.
This is about a guy making subway signs for route changes and other such situations with duct tape working for half a day or more to produce one, and a suggestion that the same job could be more easily have been done much faster (and at a similar cost) with some desktop software (even Word would do it) and a plotter or a simpler laser printer.
The second suggestion is not just not outlandish, but also how such signs are done in tons of businesses and organizations all around the world.
Dropbox case:
Complex domain, difficult to simplify, main selling point being "works out of the box" -> Suggestion of a nerdy, ad-hoc process, that needs elaborate setup maintenance
This case:
Trivial domain, done in a labor intensive personal manner with lots of needless manual labor -> Suggestion of a much simpler, most common way businesses/orgs do it
You could argue that doing it with printing misses the quirkiness, personal touch, uniqueness of the process, and I totally agree.
But not that this process can't be automated and replaced with a simple PC+printing for less manual labor and low cost.
I've done it for a couple organizations I've worked at, and it's trivial. You can print black and white A0 and larger signs for a dollar (and color for $10 depending on size, up to A0 which is 33.1 x 46.8 in).
In fact the whole point of the article about this Tokyo subway guy, is that it's a unique case because this (duct tape and hours of manual labour) is NOT the way such things are usually done.
This is how thousands of small businesses and organizations the world over produce signs. What seems bizarre to you?