In their defense, Google does try to be as transparent about these legal obligations as possible: http://www.google.com/transparencyreport/userdatarequests/

Google do in the context of law enforcement.

Very little information on the security services (e.g. NSA).

Skype's primary business is (video) telephony and IMs. In most cases, these are far more likely to contain sensitive data than the others you've listed. Google rivals it with Gmail of course, but Google also has very transparent privacy controls and makes it simple to know if you've cleared your chat logs, disabled things like Web History and Search History, removed certain emails, etc. Skype is completely opaque on such matters.

Honestly I'm uncomfortable using anything except a local Mumble server for VoIP telephony. Been using Google Hangouts recently for video calling, but would be interested in a Mumble equivalent for video.

Given Microsoft's track record for security, questioning the competence of any of their offerings is just good sense and due diligence. Given Microsoft's track record for honesty, questioning their motives is also good sense.