Good info there, thank you. I can imagine that heavily client-side CMS systems are pretty rubbish for SEO. But the vast majority seem to be written in server-side PHP. Some of the bespoke ones might confuse Google's spiders if they're written badly, but by using one of the big names, I'm guessing that there isn't a huge difference in SEO capability when in the hands of a good SEO person.
For example, I can't imagine people saying "Don't use Drupal, because it makes SEO difficult". It would be like saying, "Don't buy such-and-such car, because the wheels tend to fall off." Good SEO is such a fundamental part of a public-facing website, it's surely a must when someone creates a CMS system that's intended to be exposed to the public.