That obviously ignores inflation. Microsoft's peak of $619 billion in 1999 would be about $851 billion in 2012 dollars [1]. As such the word valuable is out of place there.
This article just seems like a rushed and careless attempt at pageviews. I wish people didn't upvote submissions like this.
I think that the labels for the graph have been swapped up. Microsoft (1999) and Microsoft (Current).
Yeah, that was super confusing. At first I thought it was adjusted for inflation but then I saw the current numbers as being lower than the old numbers and didn't know what to make of it.