Google's ad mechanism reads all emails sent and received by all gmail users, even in many cases people using paid Google Apps mail unless the administrator has opted out (I've encountered companies that left gmail ads enabled). This means that to a degree, the privacy and security of all your emails is compromised - though we would all hope that Google firewalls that stuff off carefully and ensures that no traces of the mails remain after they're scanned for ad keywords.
To say that Microsoft accessing one account based on evidence in order to gather more evidence for a civil suit - with explicit permission granted by the user during signup - is equivalent to Google's behavior is just blatantly wrong.
Both behaviors may be undesirable, but they are very, very different.