Every competent programmer should be familiar with basic security principles. It's then your responsibility to educate yourself about how to apply those principles in a given situation.
I can confidently say this because I'm a web developer in a studio of game developers and most of them don't even know how to run mysql locally. They aren't stupid, they could, if they spent the time to learn it. But they are much more interested in improving the efficiency of their A* pathing algorithm.
Regardless, the super meat boy developer made a pretty basic mistake, which you could perhaps defend with your argument, but he then refused to engage with someone who was reporting a vulnerability and trying to help. To me, that's pretty astounding.
This is especially spooky since MySQL contains a few scary features like System() not to mention that anybody could connect and write a script to do massive crossjoins (as indicated in the original thread) I'm sure any decent game developer would understand the implications of O(n!) but they were probably blissfully unaware that these features even exist.
I doubt that Notch would have made such a schoolboy error :)
He made an equivalent one: he wrote his own database[1], in the age of SQLite being dumb-as-dirt-simple to use and MySQL almost a no-brainer.
[1] - http://notch.tumblr.com/post/1166302589/this-is-what-im-doin...
Throughout Minecraft's development, "barely good enough, and sometimes not even then" has been the externally visible modus operandi. That so many players put up with customer abuse is unfortunate, not least because others will consider Notch's slipshod development practices and infantile product management goals to which one might aspire.