Questions that ask for where to buy particular items (sometimes even in in particular locations) will likely get out of date eventually, as stores close and websites fall into disuse. It's easy to say we shouldn't allow questions that elicit such answers, not so easy to enforce (and I really wouldn't want to enforce such a policy).
Stack Exchange discourages answers that are likely to age badly. Unfortunately, a lot of cycling expertise lies in knowing where to get, say, a 9/8" yellow teflon-coated framijamit for a road bike, or what framebuilder is the only one who makes pink tandem carbon frames with braze-ons for commuter mug holders. Questions like these represent real problems, but would be difficult to answer with how-I-know-the-answer other than "I happen to know this".
How do we identify questions likely to get out of date within a few years? Should we use the tagging system to track them? Close them after a year? Keep updating them?
Do we find a way to revisit likely-to-age-badly questions on a regular basis? Do we discourage the most egregious likely-to-expire questions?
(I was originally writing this up as part of my answer to this meta question, but I think it's really a separate issue.)