Have any numbers to back up this assertion as opposed to sales figures of iPhones, iPads, AppleTVs, Macbooks, AirPorts, etc. - all integral fixtures in the smarthome ecosystem?
> integrating the Echo with Plum's Lightpad is extremely easy
Amazon does not have tight enough control over its smart home ecosystem. While it may be easy for you to integrate your thoroughly designed and tested product, it's also easy for shady vendor x to integrate their cheap, disaster of a product, and Amazon will not expend the resources to vet it, but in the end the user will blame Amazon when that product catches fire because they branded it as OK to work with Amazon products.
Apple doesn't want an outside dev ecosystem building up around its products before its in a position to tightly vet and control what engineers create to enhance the ecosystem. Third party applications/devices are an integral part of the user experience, and by extension, the customer's feeling towards Apple as a brand.