[d0]

That's just logical. Windows uses loose code signing. SmartScreen is the same sort of thing but you have to buy a more expensive code signing cert from VeriSign etc. You can self sign or run a CA on windows domains, even for metro apps on enterprise edition (and RT).

OSX is easy enough to control via spctl as well. You can use this or pay $99. Several things I downloaded, including Logic Pro from Apple didn't come with a certificate. It's not a big deal.

Most of what you say is paranoia. Signing is overall a damn good thing.

Android is. If you flick a switch. Same with OSX and Windows. WP even allows you to install unsigned apps if register it as a dev handset. Same with iOS.

This is mainly about protecting both the end user from malware and protecting the app sellers' revenue stream.