Regarding ISP-side filtering, although in practice I think that all the Jewish services require human intervention to modify the filter, theoretically the ISP could setup a simple administrative password-based login to add sites to the filter. But even in such a case, it would still be more difficult for a non-administrator to hack around the filter compared to beating a local system based filter. Though as far as self-discipline for the admin himself, it would be all-too-easy to allow oneself past the filters via the administrative access.
