If anyone doubts that, this very browser used to read and write is built all the way up with dozens of libraries from compression, network, image encoding, decoding, video encoding decoding, encryption, graphics, sound and what not where each library is totally separate and sometimes was never intended to be used to build web browsers by the original authors.

Rest assured, most of the business (or web 2.0 systems, search, curate, recommend, surface etc kind of) systems are a lot more simpler then an A class browser.