I would also point out that Qwest does this walled-garden approach for
their customers (have been for at least 5 years now? DonS@qwest could
clarify) and they've seen success with it. Aliant in .ca also has some
fairly aggressive anti-malware works installed. There are places
where this sort of thing works well, planned and engineered properly.
I think Qwest, at least, made some of their reasoning and design/goals
publicly available for a time as well.
I think Jonathan Curtis did something similar at Bell, but I only spoke
with him about it for a couple of second two years ago, as Rio was
rather distracting. So am unsure.