[nostrademons]

A lot could just be that the requirements are very different between HPC and typical message-passing business apps. In HPC, you want to squeeze every ounce of performance out of the cluster, by definition. If you could get rid of the message-passing overhead, that would be a huge speedup.

For most business processes, you don't care about performance all that much, you just want things to be easy to change. Message-passing works fairly well for that: it's easy to understand, composable, and let's you swap out one component for another as long as the interfaces are compatible.

BTW, message-passing isn't exactly untried. It's the basis for the service-oriented architectures that underlie Google, Amazon, FaceBook, and many other large businesses. It works very well for that problem domain.

[kenjackson]

The message passing issue with HPC codes wasn't perf overhead of the messages. Rather it was that developing message passing applications was very complicated. But message passing apps, when written correctly gave very good performance.

With that said, you're right. If you don't care about performance, or if you have very large grains of computation then message passing is relatively easy (although so is just about any model with those requirements). The question is what about when you actually do care about performance and your grains aren't so large that doing communication half-way across the planet isn't acceptable? When I'm trying to get 60FPS in my physics engine, I probably don't want to use a web service interface.