This is definitely good email sender behaviour, but I would hesitate to purely put this down to the altruistic notion of 'keeping your inbox tidy' - Inbox Zero is a problem fairly isolated to the Newserati and similar thin slices of population.

Fact is, Email Deliverability is increasingly engagement-driven these days, especially with the major ISPs, and additionally sending email costs money.

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At its most basic level, a sender's 'spamminess' is determined by percentage of spam reports against overall deliveries from that IP. Levels over 1% put your reputation in the 'severe' category, and risk lack of inbox delivery, blacklists and more. Having more engaged users leads to a better ratio - for this reason alone keeping your recipients 'fresh' is valuable.

Additionally, another common pattern of email (or more correctly a sender:template combination) falling into the 'spam' category for an ISP is to see a few percentage points in drop, followed by a complete /dev/null-ing. When the initial drop happens, whether or not your recipients correct that as a false-positive will determine whether you get the Full Monty. Naturally therefore removing the least engaged users has a significant beneficial effect on overall deliverability.

These days though, it's getting more complex, nuanced and ultimately more individual.

Gmail moved some time back from a centralized concept of 'spam' to a much more personal view by using your positive and negative engagement signals: opens, clicks, replies, 'delete without reading','report spam' etc. They explicitly modify the visibility of email in your personal inbox through the 'important' flag (http://support.google.com/mail/bin/answer.py?hl=en&answe...), but there is good evidence that negative engagement can carry an email all the way to the spam box for a given user and consequently affect the overall deliverability.

This has a strong benefit for Gmail in that they become much harder to 'game' - something Google Search team also has plenty of experience in avoiding. They essentially eschew the classic SMTP 5xx return codes for 'Accept All, Ask Questions Later' in all but the most egregious cases, and provide little to no feedback for senders to troubleshoot delivery problems on the basis that if your users want your mail, it would be getting through.

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The second primary motivator here (still with me?) is that sending email also has a non-zero cost which is almost entirely driven by sheer subscriber count and delivery attempts.

Consider a typical mass-marketing email with a 10-15% open rate, delivered multiple times a month. Even assuming a varied engagement profile that mailer is engaging with at most 50% of their list over the month. A simple list of 1MM recipients would incur an increased cost of a couple of thousand dollars a month to send into the vacuum of disinterest.

There is, in certain circumstances, a benefit to be gained from 'eyeballs on subjects' for brand awareness, but that metric is near impossible to track, and as mentioned above unopened emails can be deleterious to your overall delivery to the more engaged segments.

For both the reasons highlighted above, mass-market email has been using the 're-engagement' method (breathlessly described in the OP as a customer-driven action), to keep their lists fresh and costs down.

I do applaud the application of metrics to provide intelligent subscription management. At PostageApp we see the best delivery rates come from our clients who take active interest in the concept of humans at the end of the SMTP pipe. The growing provision of engagement data through APIs is helping drive solutions like FAB's, and the end result is a better experience for the user. That said, this particular innovation came not from the consumer-friendly high visibility consumer and SaaS markets, but has been around for many years in the risk-heavy line treading bulk marketing industry.