[mooted1]

Sharding your application geographically is a quite a bit of complexity and requires a lot of work developing support infrastructure to manage load balancing, failover, and placement. One of the advantages of SOA is that different services can have different architectures.

To be precise, we do do geographic sharding in the services that benefit from it, but avoid it in the services that don't.

Also note that the assumption of region based partitioning doesn't extend to all applications. Analytics, for example, may want to dice and slice the data along different dimensions. Partitioning is a convenient abstraction for managing marketplace scale, as you mentioned, but inconvenient elsewhere :).