> However I don't know if that reflects some deeper truth about the world, or just my bias in how I answer the questions.
It's the same reason why you always end up on "Philosophy" if you're browsing Wikipedia and consistently follow the first link in each article. Here's the path for "Airplane":
Airplane
Fixed wing aircraft
Aircraft
Vehicle
Motion (physics)
Natural science
Science
Knowledge /* we know where this going... */
Fact
Proof (truth)
Argument
Philosophy
It's the same reason why you always end up on "Philosophy" if you're browsing Wikipedia and consistently follow the first link in each article. Here's the path for "Airplane":
Try it yourself: http://www.xefer.com/wikipedia