Edit - In the wild, a 503 usually means that the person who built out the site did not do a very good job of estimating traffic. An empty response can return 503 if the server is overwhelmed with connections.
In other words, a 503 more likely than not has nothing to do with code and has everything to do with provisioning enough resources for the amount of traffic received. Unfortunately, that's a tough thing to get right, particularly when you land on the front page of Hacker News during extremely busy times.
Now I know, that it can be easily a cause (out of the many) when owner simply "suspended" site for a while, and fixing stuff.
Thank you.
If you're interested in taking this further, it's a great chance to figure out how you would:
a.) Deal with a 503 if it happened while your site was under heavy load.
b.) Harden your site to avoid 503s.
Have fun and thanks for your kind response!!