I've been trying to find on the web some kind of summary/document/table which would quote the number of GPUs per Intel family/model/stepping. Anybody has some useful pointer ?
By "GPUs" I assume you're interested in the number of parallel "EUs" that are available in the one graphics device. The Media SDK abstracts this information and treats the device as a single entity (and internal code is optimized to make use of available resources). The EUs are not the only components used for MeidaSDK tasks.
Other APIs (like OpenCL or DirectCompute) that are designed for parallel execution have methods of reporting the number of available EUs.
I do not know of any 'offical' table listing all of Intel's products, as there are many "SKUs" and a wide variety of implementations. Using the MediaSDK API allows application to work well on existing products, as well as future products.
This is a "Media SDK" support forum. While other hardware vendors may have other documentation about other APIs, I am not seeing any question about Intel products here. The hardware implementation of the MediaSDK is designed to support a 'session' that makes appropriate use of hardware resources (which are very different than the resources of other hardware vendors). While the Media SDK 'works with' other APIs, there is not a MediaSDK API for "GP GPU" programming. (Implementation of MediaSDK may or may not use general-purpose or fixed function hardware resources). If there are unrelated questions about Intel support for other APIs, please direct them to the appropriate forums.