If you use "common size financial statements" technique (e.g. in income statement everything is sized as a percentage of revenue), you will see that COGS ("cost of revenue" in their statements) as a share of revenue grew: 47.7% in 2011, 56.8% in 2012, 63.3% in 2013. That was partially offset by a growth in sales, marketing, general and administrative expenses (SG&A) that was slower than growth in revenue.