Every time I try to post something other than this (if it works), I get...

Spam detected. Post was deleted.

Why?

Out of necessity, we have a rather aggressive spam filter that looks for (amongst other things) certain... naughty words that tend to show up in spam posts. It works pretty well most of the time. For the 4000 or so user-contributed posts on our web site, we've automatically deleted more than 400,000 posts. Yes really: more than 99% of all posts here are automatically generated spam posts. Probably 10% of the remaining posts that get through are hand-added spam that gets through the filters, which we have to delete by hand. And, rarely, someone inadvertently triggers the spam deletion by accidentally using a common spam word, so our apologies, and please look through your comment and see what's triggering it. The strangest example ever to trigger the response was the word "wristwatch." That one took a long time to figure out.

One of the URLs that I need to post has ex-ex-ex in it. Plenty of other websites keep forums clean without such draconian measures, have you considered alternatives? Making it hard for people to use the forums can't be good for business*.

* - the post I am trying to make is regarding relative qualities of 8x8 RGB LED matrices, including one that you sell.

If you think that a spam filter is bad, you should see what a forum completely over-run with spam looks like.
And, we're pretty far from draconian. A keyword filter is a heck of a lot less oppressive than many of the other methods out there. Note that we allow anonymous users to comment, we don't hold comments or forum posts for moderation, both of which would be more foolproof but indeed draconian.

Anyway, if you have some URL that isn't suitable for young eyes, you can hide it quite effectively with TinyURL or similar services.