Re: I only just noticed...
"For the <www.thereg> subdomain they're not doing redirects to the HTTPS version, so you can browse to http or https and both work.
<forums.theregister.co.uk> do have redirects enabled, so if you try and hit the http, it will bounce you to https."
Ah, makes sense. I wondered why the main site suddenly started using https right after I posted that comment. I guess I have an out of date bookmark that gets me to the http site, but visiting the forum and then hitting the top banner to get back to the main site hooks me into the https version.