1. AFAICT, the UUID test is solid; the platform test somewhat less so. But there is no way to assess infection in a computer that's off, or not connected to the internet for whatever reason. So no, there's no 100% certainty in this test.
2. The UUID check is just another option offered by a commercial entity, albeit a rather unique one that will certainly appeal to a subset of Mac users out there. So no, it's not strictly necessary, but yes, people will use it. Heck, I did, if only just for giggles.
3. Yes, Little Snitch will let you know who's calling home, and you might notice and even recognize malware comm attempts if you don't respond reflexively to the LS dialogs. But I wouldn't bet the bank on that. In reality, however, you will never see those dialogs, because the mere presence of LS will make the trojan abort its infection procedure and erase itself.
As to Apple offering a detection/removal tool, this has even more of the advantage I mentioned above in item #2: an officially sanctioned tool from 'Olympus' itself. That said, I'd like to point out another aspect of the cleanup effort: it has been mentioned that the proliferation of detection/removal tools opens an opportunity for malicious abuse. It's conceivable that such a tool could harbor malware itself. That suspicion/possibility is less likely with an Apple product.
