That's in 2013 not 2008. And remember that the costs for DDI are low - so the profit margin is huge.
You mean when they brought out 5e? Because that's the way it reads to me. 4e was when they decided to try something new. Not looking for the first high so much as an entirely different approach. It was a bold strategy, switching to online.
That's actually a fairly common myth, costs for online only are not cheap. It only becomes cheap when the number of users becomes very large because costs remain relatively constant with online while each customer increases cost offline.
To do online you need...
-Web designers
-Database Dev
-DB Admin for maintainence
-IT to keep the servers up
-Servers
-Electricity and cooling for those servers
-Customer Service
-Offsite storage contracts for DB backups, especially for financial records
-Ongoing development costs
-Credit card agreements and processing fees
-Bandwidth costs
-Then factor in the hidden costs: Legal for the various agreements, HR, any localization, etc.
These costs remain constant up to a certain point in terms of number of concurrent users, while producing offline material scales with each customer as you need physical goods for each. The problem is, you need large numbers of users for those costs to become cheaper than the costs of producing physical goods. With volume as low as DDI had, the profit margin likely wasn't nearly as good as people think it was. It's very likely DDI was costing $1,000,000 to 1.5 million a year to operate.
Also, IIRC, 2013 was when they had their peak number of DDI subscribers from what I've read. So if true, 2008 wasn't all that great.
How do you know that 4th edition was when they tried something new? How do you know 4th edition wasn't designed around increasing per-player expenses such as via DDI being nigh mandatory, miniatures being nigh mandatory (And sold conviently randomized), and Everything is Core making the purchase of all books and DDI nigh mandatory? How do you know that 4th edition's design wasn't based on a directive to make it different from everything OGL'd?
I frequently see the statement that 4th edition was designed to be "New", "A better D&D", but what I'm seeing indicates to me that the design of 4th edition was all about increasing per-player expenses and since Heinsoo has recently used the term "Rebranding" to explain 4th edition's alignment I have to wonder if all of 4th edition's design wasn't "Rebranding" instead of "Improving".