It says in the article that "In 2007, only 3 of the top 20 websites were able to achieve 5 nines or 99.999% uptime." Among the top 3 was Myspace. Which is funny because you need traffic to worry about Uptimes...
Zero down time by Yahoo is, quite frankly, astounding. Kudos to their devops team! Not even Google made that (though I bet they can now).