Actually a few years into the industry, I would doubt any body who claims to know these things straight out of this heart(Unless that is his day job).

Seriously do people remember all this math all the years they are building software? Unless you spend a great deal of time revisiting these concepts every other month, there is no way this is all going to be in your head. And if you actually are spending that amount of time learning this kind of math, I would wonder what kind of a programmer you are. A programmer is supposed to build things in this time, gaining mountains of factual knowledge which doesn't have much value in the real world is not very good use of time.

By the way this algo/DS love looks very similar to tool religion. People focus too much on tools used to solve problem, while they should actually be focused on problems.