On the philosophy or the difference, you've really hit the nail on the head with respect to the principal differences between the private sector legislation, where it concerns a consensual relationship, and the public sector legislation. When you're dealing with a bank or dealing with your local video store, you have the opportunity to go elsewhere, so consent is really the bedrock of it. It's about informed consent, and that links to principle two and principle three within PIPEDA.
A citizen does not have a voluntary relationship with the government. Perhaps when it comes to certain services and whether the individual chooses to take advantage of those particular services, there is a bit of the voluntary, but a citizen's relationship with Revenue Canada, the employment insurance commission, or other departments is not voluntary whatsoever. The individual has an obligation. One can't necessarily ask for consent.