Sure, their VC firms might do the due diligence, but Giga Entertainment (in the article) has a form D showing there were at least 179 accredited investors who acquired shares. There's a lot of people not doing due diligence that you can defraud.
VC's always say that. I'm sure some do more than superficial due diligence, sometimes, but honestly I don't really believe them, at least not in the early stages. For companies at those stages I wouldn't be surprised if more than cursory DD had a negative ROI anyways.
Yep just look at Clinkle and (in particular) Theranos