It is not possible to generalise...
Unfortunately, yes I am generalising, and I'm mainly keeping my generalisations aimed at the traditional HTML sitemaps, the ones you see on websites where there is a link at the bottom, and it goes off to either a one page html site with many links, or a multipage sitemap, still with many links.
These html sitemaps are typically autogenerated sitemaps. What I'm also seeing in the SEO community (this thread is in the SEO section of the UKBF site) is a growing trend of the big mass-market SEO companies (same SEO strategy for all clients, XML sitemap, HTML sitemap, add blog, etc) adding HTML sitemaps and XML sitemaps to sites (whether they need them or not, whether they are
detrimental or not), all generated by the same tool (e.g. the xml-sitemaps.com tool). And I'm personally not a fan of this practice.
I may be generalising, but I'm not generalising as much as Matt Cutts, which was the main point of my feedback to the OP in my initial post, since Matt is basically saying html sitemaps and main primary web navigation systems are the same thing, which I think is confusing. Matt talks about the sitemap on his blog, but in reality he is talking about Wordpress's main navigation system, there is no HTML sitemap is the traditional sense on Matt's blog (have people actually looked at the OP's video, which is the main topic of this thread). So what Matt is really saying is that having a decent search engine friendly main navigation system is what is important, not a HTML sitemap in the traditional sense.
Unfortunately I can see this confusing video and the resulting scanning over of information, or mis-reading of information or chinese whispers as going only one way. That it is perceived by the general public that their sites must have these really important HTML sitemaps added, otherwise their sites wont rank. And I can see the mass-market SEO companies jumping on the bandwagon reinforcing this myth to sell their services, some SEO companies are already doing this. A similar situation exists with XML sitemaps.
It doesn't matter what size the font is to a screen reader.
I personally do not think that HTML sitemaps in the tradtitional sense are that screen reader friendly:
1. A link right at the bottom - so the blind user has to tab through all the links, listening to all the links being read by the screen reader, before they get to the sitemap link (yes I know Alt-Tab might do the trick in some cases, or shortcuts)
2. A sitemap page with hundreds of links on it, each one being tabbed through and read out by the screen reader before the user reaches the one they want. In these cases a primary hierarchical navigation system (showing a few links at a time, allowing the user to drill down) is more beneficial rather than big sitemap pages with lots of links.