Sounds like the salesman either didn't know about member4member, or wasn't able to sign you up with it.
I know someone who did this recently, you just phone up to order it and tell them the person who referred you over the phone. You both have to watch your bills though - cablecom may forget to pass on the bonus and might have to be reminded.
As Lob already said - you'll still need your Swisscom line if you want to go with ADSL. Sunrise might give you the ADSL modem, but Cablecom will always supply the cablemodem anyway.
You probably want to add a router to it anyway, and wireless routers can be had for under 100 francs anyway.
The nice part with cablecom is being able to say bye bye to the Swisscom line

And anyway - did you read today that the government has buried their plans to privatise Swisscom, so throwing money their way is just propping up a state-run telecoms company...
Of course if you are really into saving money then you could avoid the extra 20 francs for digital phone and get a true VOIP phone - 044 numbers for 1.50 per month - just check Lob's signature