One thing I've noticed is that most web jobs 90%+ ask for library experience of some sort.
About 10 % do not... they focus more on the language then language-libraries.
Why this lean toward libraries? I can understand that you don't want to have to re-write AES encryption algorithms and PHd level math things like that, but so much web development does not have any high level math at all.
What is the difference between jobs that focus on library use vs. jobs that focus on language?