With all due respect, let me express my professional POV [in advance, no offense intended, even if my language seems to be harsh
] :
1. Just because A stands for Apache in the name of package, and thus you can't replace it with any other web server software, honestly is quite a LAME excuse. And this also shows your lack of knowledge about the high scalability and the needs today's IT work demands. Let me give you some fast facts re today's IT world, again humbly and with all due respect: We live in the age of social media and social information networks and an IT expert without sufficient knowledge and skills on the technologies that enables us to facilitate today's IT structures, at best is good for nothing... No respectable IT company gives rat's ass about what university you graduated from with what grades, but your experience on stuff that matters today. And they are cloud computing, social media, heavily loaded infrastructures on the web or otherwise that are adequately configured to survive the weight they receive and live to see another day in this competitive market. So forgive me if I keep insisting on these stuff, like memcache on PHP, nginx etc, to be incorporated into XAMPP. If the owners of this project are just fine with their package of most basic tools, the audience for which consists of low profile, junior developers - then I guess I have nothing to contribute here... But no, if they aim for higher standards, if their goal is to build a package that provides the latest cutting edge technology for today's web development needs [regardless how "basic" and small that package is], then I am pretty darn sure they will tend to agree with me...
2. Talking about market shares and throwing numbers to people's faces isn't really a convincing way to go - because if numbers really mattered, Chrome would really be considered a superior browser to any of its competitors, because it has the biggest growth rate in the history of web browsers, than any of its predecessors. But we all know that Chrome only has its superior speed, but not because it has superior technology, no, but because it's just an empty shell. A browser which can't even display an XML document in a decent way. The only reason it is faster is because it lacks most of the important features other browsers do. It is a great browser for an end user, but that's it.
Talking about Nginx the same way, is as uneducated attitude as in the example above... You can't look at those numbers and make decisions on the fly. Every experienced developer/programmer/Internet professional knows how hard it is to scale a heavily loaded web application, and the value of Nginx and other similar tools which are enormously helpful [and free at the same time]. From technical stand-point, Nginx is superior to all proxy servers and light-weight web servers when it comes to "price over performance" ratio, and it quite easily overcomes MANY bottlenecks Apache can't, which makes it superior to Apache in most cases... It is totally customizable, its configuration syntax is much easier to master and its features are richer in overall quantity and quality; and it is easier to install and run. Almost none of the high-profile web projects facilitate Apache, since it's very heavy-weighed server and not scalable when hits reach tens of thousands per second. I can go on and on, on this one, for hours, but I am pretty sure you got the picture...
3. I didn't say "let's replace Apache with Nginx". It can be a second [but powerful, yet] choice for those who wish to facilitate it.
So, in short, it really doesn't matter to me whether XAMPP has Nginx in it or not. I am already using it this way or another. All I want is to provide professionals with tools that matter in real life situations, not something upon which you build your "home page". Thanks...