Exactly! In a public space, you can expect someone to be collecting data about you, even if it's only photographing you in the background. In a private space, you expect no one to be collecting data about you, except the people you are directly interacting with.
Aren't there some wiretapping laws around this sort of thing?
This seems a bit analogous to the treatment of attorney-client privilege (at least in the US.) If I have a discussion with my attorney in my house, or in my attorney's office, with no one else there, the conversation is generally privileged. If I have that conversation in the presence of a third party, the conversation is no longer privileged. So, if I'm in someone else's house, I may have implicitly consented to the fact that I don't control the environment and can no longer assume the same level of privacy.
(IANAL, YMMV, etc.)
A home may be a private space but it isn't <i>your</i> space. When entering someone else's space you open yourself up to having to abide by their rules, listen to their music, and be captured by their cameras.
A business is typically located in a public space, where there is no expectation of privacy. In contrast, a home is by definition a private space where there is a strong expectation of privacy.