That's a linear extrapolation from the last two data points on the graph, but it seems to be growing super-linearly.
I work for Amazon (and wrote the blog post referenced by GigaOm), and I certainly won't speculate (or place a bet). However, note that the growth from 262 billion to 449 billion objects took place in 6 months.
I'm calling 1T+ objects for Q2 2012. The S3 object count is growing by between 150% and 200% every year.