All software we use is "at risk". EULA even says so, as in 'not warrented for any use'
I don't think Avast is encouraging us to stay on XP, just being realistic instead.
Problems created due to the software (bluescreens of death, freezings, etc.) are not equal to problems not prevented by the software, but promised to prevent.
However, the most quoted part from the blog so far, might imply that Avast would be able to cover for all
"AVAST will continue to support Windows XP users by creating protection modules and detections to cover vulnerabilities and other security problems for at least the next three years."
Some people here actually believe that by installing Avast and using Chrome (or any other still supported browser), they would fix every security issue in Windows XP after the end of support. That's the frightening part.
Another is that there are so many people here who would rather recommend some "security software" than to plea for prudence to at least switch to a live Linux system for online access and playing all those retro-games offline.