This may qualify as fair use, and in any case it's not like this is going to jeopardize sales of the 29 year-old Super Mario Bros or any of it's derivatives.
It's as if every line of code written needs to be useful. I'm seeing this more and more. Many cool projects are criticised based on how useful they are rather than how cool they are. Maybe if a project was positioned as useful/sellable, then perhaps such criticism is justified, but when something is obviously not meant for sell and has obviously been built for all except seriousness, it just comes across as daft.
Just the other day I saw a comment about an embedded PHP interpreter. "How will this EVER be useful?" Who gives a shit? It looks fun to write, so it was written.
I personally enjoy programming. Most code I have written has made me 0 money, has been seen by 0 eyes and has provided me hours of fun and pleasure in writing it. I'm sure many programmers are the same.