I half agree. The grow of the final version is not linear, but I guess it's still like sqrt(time) or something. There is a lot of refactoring and backend changes, but also there are a lot of obscure "features" that accumuate.

(It would be nice to make a study about the number of LOCs in Chrome or other big open source project. LOC is not a perfect metric, but it's better than just guesing.)

Word has a compatibility configuration window with a lot of weird features, like (totally made up) add 3 pixels if a bullet list starts a new page because it was the default in WinWord 1.7. And there are like 10 of to mimic 10 versions and perhaps even other editors.

Also, a log time ago Word has a "feature" that converted automatically every acronym into a "Mini Card" or "Smart Card" or something with a dotted underline and a rectangle that appeared when you put the mouse over it. It was annoying. There is still code to show them, and perhaps even code to create them.