I'm not entirely surprised. MS never does anything unless it benefits MS.
MS doesn't spend half a decade planning and coding a totally new operating system just for humanitarian reasons.
"Oh, the people need a better, OS, let's get on it!" are the words that never will come out of MS's collective mouth

As for AV software and the like, MS AV is a joke, like many components of their OS. I turn off the stupid MS security center the instant it starts warning me I've turned off the stupid MS firewall, or the instant it starts warning me that I've turned off the windows autoupdate.
Maybe instead of "typical" and "custom" installs, they should add a third, named "I know diddley squat about PCs" and then have this stuff enabled by default for that install only, but for those amongst us that are actually semi-competent, it's more of a hassle than anything else.
I think it's still far too soon to be sure about other AV software. I think the people will demand it. My prediction is that MS will realize that it has to keep the folks happy or they won't use it, and to make them happy it needs to allow 3rd party AV.
How long it will take them to realize that? *shrug*