Ignore /u/CorruptedEvil until they make a more, lets just say informed comment? There are different methods of implementing vertical sync, the game may wait for the entire frame to be rendered causing issues with FPS, or the game may implement triple buffering in order to buffer up the next full frame instead of waiting. Triple buffering it typically an option seen in a lot of PC oriented AAA titles, and is also something that can be found in various GPU control panel settings which can be forced on manually (but may not actually force the option to be on).

Why do developers not implement consistent well working Vsync? For many reasons including not caring, time constraints (which kind of go into the not caring area), and lack of real software engineering experience (typically game devs are bad at even the most basic of software engineering principles including modularity and code re-use). Game devs have very insular software engineering experiences, typically only working within one company or only in the games industry, where, though working harder than other locations, aren't exposed to typical business practices that have been standardized in most software engineering firms. They are paid significantly less especially if you consider the areas they work at (60k in California? Wtf?) and it really, really shows.

When people bring up A* jump as a "new novel" path-finding algorithm at conference because they haven't read the most popular CS research papers from 50 years ago, you know there are some issues going on.

The age when small groups of genius programmers would make excellent game engines that would push the hardware limitations of the age are pretty much over. Replaced with old hat stentorian programmers highly resistant to change and numerous licencing constraints on software for deals that were supposed to "speed up production" but only end up creating inferior products and slowing down development time in the end due to legal constraints.