Note that the theregister.co.uk link points back to ircmaxell's blog.
The SO link is for an answer from 2009, pointing to an email from 2006.
ircmaxell's blog is spot on - if you actually bother to read what it says. Not keeping a very important part of a webserver up to date with security releases is insecure. Is that a surprise to you, or anyone?
Is Windows or OSX or Linux insecure because they have security patches coming out all the time? What's insecure is user behavior when they keep running old, unpatched versions of software.
You're spreading FUD, repeating words and showing links without actually taking the time to understand the message they are trying to convey.
Case in point: PHP being "heavy". A PHP app can be as lightweight or as heavy as you need it to be. The more you build and the more it does, the "heavier" it becomes. If you throw a proper caching solution at a codebase, it becomes much better, but this is true for anything.
Look at the TechEmpower Benchmarks [0] - PHP raw is usually towards the middle, upper-middle of the pack. Of course, it gets handily beaten by compiled and multi-threaded languages.
Well, my use case is neighbour/friend websites (I'm not really a web person, but I "do computers", so I get asked a lot). Buying a $3/month domain with PHP webspace, slapping this and some HTML on it and basically being done is simple for me. I mean, compared to a "real" CMS... YMMV, of course.
Is it really impossible to get Python hosting (or better) for $3/month?
I remember that here in Europe, you can get an own virtual machine for roughly $5 to $8 per month, and Python webhosting must be less expensive than that to compete.
If you buy any webspace it will have PHP installed 99% of the time. There is a huge number of garden-variety webdesigners that server small businesses. These people are used to a combination of PHP + Apache + MySQL + phpMyAdmin. They can install Wordpress on that and know enough JavaScript to modify a gallery script to do what they want.
A Python webspace is much harder to find. Even if they would find one, they could not use it, because online resources for Python are targeted at people that either want to learn to program or already know how to program, not at people that want to use tools as building blocks.
It wasn't me who downvoted you, but if I had to guess why, it would be because administrating a full instance of Linux just to run a CMS is a long way off the ease of dropping a PHP file on shared hosting.