Including IE meant that IE became a platform that web developers targetted. A platform that was only available on systems that Microsoft decided it would be, and so they used their existing platform of Windows to make IE the new de facto platform.
Putting in something like Windows Photo Viewer isn't anti-competitive because it's not being used to leverage something else. If on the other hand, it included some spiffy new format like Windows Amazing Photo Format that was only available on Windows devices, and MS started pushing that to become the new standard that they control... that's becoming anti-competitive again. If in 10 years all cameras recorded in only the Windows Amazing Photo Format, you're going to struggle to switch to another operating system if you want to still be able to access your photos.
This is why I don't see Ubuntu including as many other applications as it likes in the package as being anti-competitive. None of them are able to force you to stay on the Ubuntu treadmill forever, whereas choosing IE 10-years back resulted in most of the web being targetted at IE, and if one wanted to switch OSes it became much harder if you still wanted to be able to access all of your sites.
As the original poster mentioned I can't see how they'd be able to use this anti-virus tool to leverage anything else? Could they corner the market on viruses? Maybe, but they already have that.