From Wikipedia on ECHR:
Article 8 - privacy
Article 8 provides a right to respect for one's "private and family life, his home and his correspondence", subject to certain restrictions that are "in accordance with law" and "necessary in a democratic society"
Many Slashdotters seem to think no one has a right to privacy, but people DO have a right to privacy, albeit a restricted right such that it doesn't trump everyone else's rights. Sounds fair and balanced to me.
One of the restrictions "necessary in a democratic society" is that it doesn't trump a person's rights such as taking photographs in a public place. It's not that you have no privacy outside, it's that other people's rights for the most part trump your privacy and hence effectively you have no privacy outside. However a company does not have fundamental rights like a human, and as such a person's fundamental rights prevail over a company's rights, including a person's right to privacy.
Remember I did say that a company can keep the data with a good reason. Debt collectors get to keep your contact details for instance. Google Streetview blanks out nearly everything that could infringe someone's privacy and hence probably doesn't fall foul. I hardly see a good reason that Google would need to keep your SSID and the like.
Your impression that there is a contradiction between Slashdot's anti-privacy views (photographing a police officer or a building) and Slashdot's pro-privacy views (Google SSID) hinges on your impression that a company (or the government) has the same rights as a person (or that people don't have a right to privacy, but you know that's not true). I know you said you're from Australia but that's a very American view IMO, not really compatible with Europe.
By the way the Data Protection Act is a good piece of legislation, it has specifically helped me twice before. The extent of the complaints I've seen about it on Slashdot have been that companies can easily get around it, not that it's damaging.