> Because to a first approximation everyone understands, and can get, email, while maybe 5% of the population, if that, understand RSS feeds.

At some point in history, 5% or less of the population understood email. RSS feeds are not inherently more complex than email, in fact they're quite a bit simpler. (And even if you don't grok RSS feeds, you'll probably grok a weblog; RSS is only relevant here because it gives the exact same affordances as something like a Mailchimp newsletter, even though it works differently under the hood.)