It's only ad absurdum if you're completely unaware of the fact that UNIX (in this case not GNU/Linux, but illumos / SmartOS) is a high performing operating system with extensive facilities for preemption and traceability, which makes it ideal for web applications, and at scale, too. Haven't heard of SmartOS yet, have you, since you claim UNIX unfit for cloud applications?
Which means the OS running on the server is equally irrelevant as long as it can serve pages, CSS and JavaScript.
Which ad absurdum makes UNIX APIs irrelevant for cloud computing.