Here's a quote from Tim Bray that's relevant to the WMTS discussion:
REST isn’t good because it’s REST, it’s good because it’s good.
I get the impression that the OGC is keen to have a REST standard only because it fears missing out on the booming interest in REST and wants to keep in control of geospatial protocols. It perceives REST as a ripe emerging market rather than a distinct architectural style. This is reflected in the WMTS "KVP, SOAP, or REST" offerings, which seem like "Bud Light, Bud Dry, or Bud Ice" to me. REST isn't good because it's trendy, it's good because it's good. Loose coupling. Scalability. Evolvability. Serendipitous reuse. A real alternative to RPC.