Ive done a little more reading around this and found a few pages by MS people on this:
The WCF Web API abstractions map to ASP.NET Web API roughly as follows
WCF Web API -> ASP.NET Web API
- Service -> Web API controller
- Operation -> Action
- Service contract -> Not applicable
- Endpoint -> Not applicable
- URI templates -> ASP.NET Routing
- Message handlers -> Same
- Formatters -> Same
- Operation handlers -> Filters, model binders
and http://wcf.codeplex.com/discussions/319671
The integrated stack supports the following features:
- Modern HTTP programming model
- Full support for ASP.NET Routing
- Content negotiation and custom formatters
- Model binding and validation
- Filters
- Query composition
- Easy to unit test
- Improved Inversion of Control (IoC) via DependencyResolver
- Code-based configuration
- Self-host