The Optical Cable (Toslink) is purely for Sound and will connect up with most Dolby Digital 5.1 Amps, this isn't a new feture and has been on the all Sky + models.
It is not essential to you viewing sky, but is obviously there as an enhancement if you have the right equipment to make use of it.
As for the HDMI lead, this is included so you can enjoy HD TV from the Sky HD box, if you have a suitable HD Ready TV.
The Component Leads mentioned (but not included) are for people with TV, which have the component inputs, but dont have a HDMI connection, or have already used it up with a DVD player or similar.
Hope this clarifies things
Cheers
Darren J