Nobody 'gets' DD, which is why I - like many others - are weary of it.
Steam, Direct2Drive etc etc are all massively over-priced compared to retail BUT, in their defence, they are priced at the RRP. It's just we're so used to paying so much lower that they seem very expensive.
It's also why I'm not keen on the Go; you can bet your life all the games will be RRP, but will be half that price at retail.
The advantage something like Games On Demand has, is that you have the choice. It's there for your convenience (at a price!), or you can just buy the discs at retail as normal.