Ah yes, the release notification discussion… I’ve asked the same question on the Marketplace google groups e-mail list (according to my archive, this was back in 2013!) and I think it has been a topic of discussion many times before and afterwards.
The default answer from Atlassian is: we have EAP releases, there is a EAP RSS feed (https://developer.atlassian.com/platform/marketplace/early-access-program/) to which you can subscribe, so we’re good.
The problem is: those resources also don’t get updated consistently. So you will create some listeners to the RSS feed only to find out the product has already shipped. The only reliable source of truth here is the JSON feeds from Atlassian Marketplace that are use by the various Atlassian websites.
BTW, this is why, after 5 years of waiting for Atlassian to fix this, I created http://iapetus.fyi