"High-availability and scalability are exciting in general but there are certain problems that experts see over and over again." - that was the first line in Canonical's highscalability.com advertorial a couple of weeks ago :-)
To be fair, it's a general truism in tech that the cobbler's children never have shoes.
Or it is simply just that WordPress is expected to work like light-weight static sites.
That assumption would have been proven wrong ... lots, and lots of times. That's why there are so many great tools (cloudflare, plugins, ...) to take care of problems like that.
Because it isn't Mark. It's Canonical...
Site Optimization 101 :P
Was that don't use Wordpress or install a cache?
The latter, I assume. Wordpress provides a lot of value that Jekyll or another site generator doesn't, but you do need a cache.