But why not have both options available? I think the reason is retailers. The game console manufacturers are still really reliant on retailers (most people prob buy games at Walmart/Target/etc) and don't want to do anything that'll make those retailers unhappy.
I don't mind the option. But how it is now, it just doesn't make that much sense to buy full games online on consoles. They cost the same as they do in stores (or more) and you can't resale or trade them.
Next gen might change that with bigger HDDs in these things. I have a 250GB in my PS3 and I have 60GB left, if I put all my disc based games on the HDD....