In my practical experience I find that to get the "aptitude" requires a lot of effort put in it. It definitely would vary depending on the person and his experiences but practicing it is very important to go forward.
They are a test of how recently you crammed for your CS finals, that’s all.
Which, to some extent, makes sense. You're basically filtering out people who won't put in the effort to get the job. Whether or not those who put in the extra effort are actually going to be better employees is a different decision.
To your larger point, data structures and algorithms are popular in interviews for the same reason Project Euler is popular - it is very easy to ask a well defined, but interesting question about core CS or math.
As is, it's more like advertising for python, then surprise java.
But those kinds of questions make zero sense and have zero value if the job is actually implementing CRUD apps in a high level language. You might as well quiz candidates on their assembly language skills too, for a Python job...
So there is obviously an ulterior motive.
