Currently, Peacock is in a preview mode and is limited to X1/Flex. It has already been announced that when it is fully rolled out, it will be available on AppleTV and XBox. I'd assume Roku and similar will follow soon. Whether or not you can use the ad-supported/full access free tier with non X1/Flex is not known yet. The normal free tier is ad-supported/limited-access.
At least in the past, Digital Starter is the general TV service, with all of the locals and most of the common cable channels. Comcast keeps renaming and creating new tiers, so it's hard to say just what is included these days.
We won't be too serious about Peacock until they offer a threshold of new original programs. We just upgraded to non-X1 HD so we'll enjoy that for a while before considering X1.
Your last link was interesting; I've copied a portion of it that suggests that some non-X1 customers can get Peacock for free...but only on their devices not their main TV. (And only if their InterWeb feed is other than Comcast.)
"Current customers have Peacock Premium (a $4.99 value) bundled at no additional cost if you have: