Can someone explain why my post-related question was closed, but another nearly identical one is alive and well?
How do I get a self-addressed envelope from Canada to USA?
Can I combine two French stamps?
(For what it's worth, just to make it clear, I don't live a Canada (plus, the item I need to be mailed to me is a certificate from a consulate I used to be under a jurisdiction with), so, this is travel related.)
As it stands, the question is about mail, not travel. The reason is that nowhere does it say anything about travel, only stamps and envelopes. :) Therefore I think you should mention the reasons behind the question, and then nominate for reopening. Moreover I believe the question is interesting because requesting consular services from abroad must be an issue that more than one traveller must have handled at some point.
On a different note, comparing with past questions might not be the optimal way to go when attempting to understand the reason behind a closure for a number of reasons. These include possible changes in the rules and closure policies, as well as different voting users with different opinions at the time. What you can do to equalise the karma is to flag the past questions for closure.
I voted to close when it came up in the queue (which means somebody else put it there). Your question was off-topic for the reasons given. There was nothing 'random' about it. While it may seem like a whimsical process, closure is a serious matter and requires an impressive reputation hurdle in order to participate.
The queue also 'injects' questions where it knows the answer. This is done to make sure the reviewers are paying attention. If you fail the test several times, something bad happens (I don't know exactly what happens but it's said to be bad if you give the wrong answer to a test question). So reviewers are paying attention.
The question you give for comparative purposes was also off-topic, but it had upvotes and an upvoted answer before it could be closed by the reviewers. Your question had down votes and this also made it amenable to closure. I didn't down vote it but considered the existing down votes to be indicative of community sentiment.
You still need to hear from 4 more reviewers though.
My close vote was correct as I see it, downvoting is not (I did not downvote) because the question is not bad, it is just off-topic.
Will I take my close vote back? I do not think so because the question is off-topic.
Anyway, Travel.SE is a community controlled site, my vote does not mean anything unless 4 more people with good reputation agree. Same thing for opening closed question, so it can not be a random action as you suggested.
For me it went like this.
While I was a member at the time the first question came through, I did not have the reputation required to see it in the queue. I read the question and determined for myself that "I've had questions about sending postcards home while on travel" so that question fit (loosely) the topicality question, and so I did not flag it as off-topic. I also did not up or down vote it at the time.
Now your question comes along. I have the reputation, and so saw it in the close vote queue. I read the question and paid attention from a topicality viewpoint. I could not see the connection to travel in your question. While what you were asking help with could have been a question a (temporary) traveler might have, it is one that (more likely) a (permanent, or ex-pat) resident would have. I simply did not see the relevance to a visiting traveler. Hence my strong consideration to Vote to Close.
Lastly, basing an argument that an (off-topic) question be allowed to remain because some older (also off-topic) question was allowed, does not make good policy. The older off-topic question should potentially be re-visited, and not just allow the newer one to remain. This is essentially analogous to "yes officer you caught me speeding today, but you missed my brother yesterday so you should let me off today because...". The rules are the rules, although the 'rules of topicality' are not quite as cut and dried as something like speeding laws.
