Al, you have no idea how much of this kind of spam gets posted to forums. Some of it is completely automated, some from real people - possibly in countries where the few pennies they might make are more significant than they would be to you or me.
Really, it's not about selling stuff to people on this forum. It's about getting links to whatever they're selling spread all over the internet. This makes their websites rise higher in google search results. Often the posts appear innocuous with no links, however they have invisibly embedded links to their sites in the message. Again, this isn't for the benefit of forum members but it is harvested by google "search bots" or "web crawlers" - automated programs that index information on the internet for use by their search engine.
As a moderator at GPSReview, I am constantly deleting this kind of stuff and banning the posters. That's a large, popular forum and there are two other mods plus the site admin. Between the 4 of us, I'll bet we delete more than 50 spam posts a day.
Take a moment and thank Guy and Ben because I'm sure they are busy behind the scenes doing the same thing. There's probably a lot more spam that you never even see because of their efforts.