Horseshit. I've used Symantec Antivirus for several years at my university. We recently switched to Trend Antivirus (for whatever reasons) and Symantec was 10x better. Trend won't pick up everything that Symantec does and it almost never successfully cleans a file. Not once when I used Symantec was it unable to either delete, clean, or delete on the next reboot a file. I've never had it not detect a virus, are you sure it was a virus and not a bad piece of malware/spyware? The other big name, McAfee Antivirus is even worse than Trend. Once you install it, its a huge resource hog and good luck trying to uninstall it.
My dad uses Symantec at Boeing and anytime they have a problem that Symantec AV doesn't recognize, they send them a report (I don't know what all it entails). Symantec is obligated by contract to respond with a fix within 24 hours. Neither Trend or McAfee will make such a contract with Boeing...seems pretty obvious why.
Almost all of the 'free' alternatives online are much less sophisticated and generate lots of false positives.