I'm sure the people using these machines that are "much older and much less powerful" than a 2012 macbook air are not expecting sites to load as fast as a newer machine, and probably don't care about the loss of less than 0.1 seconds to load time. If you're running a 6+ year old machine and expecting high performance you'd have to be insane.
Even if BBCOnline cared this intensely about performance, there are more than a few other things they could do to speed everything up. The switch from Apache to NGINX for one. I know that this takes many more developer/sysadmin hours, but if they really cared about a tens of milliseconds then it is definitely something they'd invest in. NGINX has quite a lot of support and is very stable, as well as generally known to much faster than Apache in most cases [1]. It's also not like NGINX is a hipster/unused server, it has quite a respectable share of the 'market' [2].
I also noticed on this page that they docwrite a script (probably to force it async?). This type of 'hack' is terrible for performance [3]. You could just add the 'async' attribute to the script tag and actually move it in the html and reduce the cycles wasted by a hacky solution.
[1]: https://www.rootusers.com/web-server-performance-benchmark/ [2]: http://news.netcraft.com/archives/2016/03/18/march-2016-web-... [3]: https://www.stevesouders.com/blog/2012/04/10/dont-docwrite-s...