On the possible obsolescence of research paper titles starting with "On the ..." I have observed that most papers with titles starting with "On the ..." are theoretical ones, like pure mathematics, physics, computer science, etc. Most of these papers are relatively old, though I can find a few recent examples as well. 


Are such titles becoming obsolete?
If not, when is it appropriate to use it?
As I always understood it, a paper called Zero-dimensional vector spaces claims to be an exhaustive overview of the topic, while On zero-dimensional vector spaces would be merely a contribution to the study of those spaces. So it is humility on the part of the authors.