The complexity could have been reduced dramatically if they were hosting on a modern dedicated hardware configured for their workloads. Successfully reaching this kind of scale on AWS (or any other massive cluster of exhausted and unreliable virtual generics with limited I/O) requires this kind of software wizardry on the back-end.
It would have been even more complicated if all of AirBnB was running on a cluster of randomly dying first generation iPhones.
Want to avoid layers and layers of software complexity and paying for brainy guys to run it? Pay for a nicer hardware then. Sometimes it's cheaper (and easier), sometimes it's not.
They spend so much money on buying huge machines which makes writing performance intensive code similar to writing regular code - ie if its sucks it'll still perform pretty well.
Think of the biggest financial services companies you know - all of them do this.
The article is a good start, but leaves a lot to the imagination!
