One of the main differences between the Sky Digibox and other digital receivers (including PPV types such as, for example, Canal+) is that the OpenTV system provided within the Digibox implements TCP/IP. This has taken the Sky version of OpenTV in a different direction to the rest of Europe, which is why a Sky Digibox will never be able to access European content, and why European digital receivers will never be able to access interactive content on the Sky platform; but then again the Digibox is squarely targetted at the Sky service and nothing else - for example the encryption system only exists in the Sky Digibox and is not available as a plug-in for other receivers... so in reality it is an enhancement of the service.
On the right is a close-up of the Lucent IC.
By the way, the big silver thing at the top of the picture is the UHF system; an input (pass-through) from other devices or an antenna, and two outputs one of which can carry power for the "Digilink" device.