I'm not sure that's a great example. Of course e = mc^2 is so iconic and well known that most people know it, and will probably even perceive it as a whole. Once you recognize it then no need to explain what e, m and c are.
However, most code is not that obvious, and in the real world you're probably not looking at one mystery line of code who's function becomes obvious by context - you are more likely looking at entire functions or blocks of code, maybe without comments, trying to figure out what is going on. Try inheriting 10K of mostly undocumented code, and then you'd probably be a lot more grateful that the original author used descriptive names and comments, even though he knew what it all meant when he wrote it.
However, most code is not that obvious, and in the real world you're probably not looking at one mystery line of code who's function becomes obvious by context - you are more likely looking at entire functions or blocks of code, maybe without comments, trying to figure out what is going on. Try inheriting 10K of mostly undocumented code, and then you'd probably be a lot more grateful that the original author used descriptive names and comments, even though he knew what it all meant when he wrote it.