Idea is not in 'retouching' each and every page, but in marking the cache as 'dirty', so it will be regenerated on a new request. If old page (archive) will be never reached, why should we regenerate it?
There is also such a thing, as dependancy: if, for example, I update the category name, and it is displayed at the news node view page, so dependancies are: news, category + "dead" time for the cache: 23:59:59, every day (so, I will have all 'static' time marks regenerated in any way). Old and outdated items are cleaned by cron, every X minutes/hours/days (for example, every night) and there is a special (PHP) script for that.
