Sure it does. EVERY virus/malware scanner out there has given a false-positive at some point or another. I'm not sure any come close to Norton's record, but it's happened to every single one of them out there. And Windows Defender has trouble catching a cold, let alone anything else, so you are very ill advised entrusting it solely for your system's protection.It ONLY looks for malware, it doesn't do virus, trojan, or worm scanning, those are all completely different classes of threat. So no matter how intrusive you think AV programs are, it doesn't really matter, that's the price you pay for using Windows. That's not any kind of moral or subjective judgment, it's merely a statement of fact.
And so far you've only tested Microsoft products, that seem to share a definitions file, which hopefully you can see the problem with there from a logical standpoint. Someone else has scanned this file with other programs, which are a bit more effective, and found nothing amiss.
aMSN is an open source program, so it's not really made by a company per se. It's made by a group of people who work on it in their spare time for fun. While it's not out of the question one of them could have loaded some malware in, odds are the other developers would have spotted it, then done a little community policing by stripping it out, reviewing every update that particular developer has made for anything else (or just backing out all the changes they made), then blocking their access to add new code to the program.
If you think this is what happened, one of the developers slipped some malware into the Windows version, then you should contact the aMSN developers about it. CNet is just a distributor in this case, they have no control over the contents of the file. They also claim to do virus and malware checking on everything they distribute. I can't personally vouch for that, but I see no particular reason to doubt it. Odds are when you reported an issue -- and you did more than just post a comment saying it had malware right? -- someone scanned the file, found no issues, and so wrote you off as a crackpot who needs to update their virus scanner. They probably should have responded saying more or less as such, but odds are that person is doing about 3 other people's jobs, and doesn't have time to respond to every nutcase that writes in. Just running a scan on the file probably took them away from more important duties. And while you may think nutcase is a little harsh, you did only test this with one program, and that one program happens to be the poorest performing (by a pretty considerable margin) malware remover out there. Out of all the people who may have downloaded that particular program, you don't think ANY of them had an AV program installed? Maybe also some malware removers. And you're the FIRST one to notice a problem? Seems a bit far fetched don't you think?