It's the "across platforms" part that matters here. Microsoft lost the battle in their core business (OS and Apps) when platforms switched to, first Web then Mobile. Google started with Web on desktop and successfully continued their dominance to Mobile web and apps. To add insult to injury, Google added the dominant mobile OS to their arsenal right under Microsoft's nose.
Not sure why were both downvoted. Haha. They broke the mold on advertising via internet.
The key is how and why they got there. They're diversified across platforms and entry points. It also allows them to fund their other "bets" which they don't individually report. Cloud as well.