The correct comparison is his server vs a single EC2 High-Memory Double Extra Large instance with a 3 year heavy-utilization reservation. This instance costs $3100 upfront plus $0.14/hour. The total 3 year cost for this server on AWS would be 3100 + (.14 * 24 * 365 * 3) = 6779.2, or about $188.31 per month.
Sure, its more expensive. But AWS provides an insane of value on top of the server. Like instantly being able to provision additional capacity. I wouldn't be at all surprised if, on a full-loaded cost basis, it is extremely competitive with building his server. Heck, the employee salary expense of building your own server will easily drive the cost of the server well beyond the $3100 up front amazon fee.
I love building hardware too (never had a computer I didn't build except for laptops). But my mind boggles at AWS value proposition