Currently, I do shell out for an annual security subscription -- three seats. (I just tired of all the nagging and hoop jumping needed to perpetuate free AV accounts.) In my experience MS Security Essentials etc. is just not enough.
Here is the thing: If Microsoft offered top-flight security baked into the OS for a reasonable annual fee I might spring and drop the after-market application. Perhaps a two-tier sub or no sub : Windows option A would include bare-bones security and updates, basically the status quo (no sub). Option B would include a deluxe annual security package with good native utilities and maybe a little free support (with sub). You would have a choice between A or B when you activated your OS, with the subscription offered at a steep discount. Later you could still buy into the security, but at a higher price.
I mean many of us pay for some security anyway, Why not pay the OS developer? Especially if the security suite caused fewer problems since it was native. My current AV vendor currently gives me a free seat for my Android phone. Maybe the MS sub could throw in some phone security as well if you had a Windows phone. If MS could do this -- and do this right -- then they might get on the subscription gravy train. But again Microsoft's competition is doing much of this gratis. This makes the growing success of the Chrome OS internet appliances pretty understandable. MS has a pretty tough row to hoe.