Windows still has the problem of spyware. Whether that's due to lack of security or its popularity is a matter of debate, but still, to me at this point using the internet on Windows feels like sex without a condom. Relatively safe if you truly trust what's on the other end, but definitely a risk.
On the other hand I surf the internet without so much as a care on my Linux machine. You still have to not be an idiot (ie, don't type your info into phishing sites), but I have no fear that simply visiting a particular site is going to hose up my machine.
As to the Office competitor - Office is being marginalized. Even in our corporate environment we just implemented Office 365, and when you do that you have an option: an "E1" license which has browser-based office, and "E3" which includes the full MS Office suite. We've put about 80% of our users on the browser based version and they're doing fine. That browser-based MS Office actually works just fine on Linux, and is actually far more limited than LibreOffice - it just is branded MS Office so people will accept it.
Microsoft is being marginalized. My guess is that if PC gaming survives, it'll eventually shift to Linux. I'm just not sure there will be too many people aside from geeks and gamers still using a desktop computer by that time.