You make a perfectly valid point, but I don't think it addresses the issue at hand. I think what concerns people about uBeam is that they might be the next Clinkle i.e. a case of VCs getting overly excited by a highly charismatic young founder who talks a great game and has an extremely bold-sounding idea that could make them a lot of money.

Clinkle was able to raise the biggest Silicon Valley seed round in history ($25 million) in June 2013 with a non-working demo for a mobile payments app that had an admittedly beautiful UI and could be used to pay retailers with high-frequency sound technology, the type of technological concept that probably looks/sounds like magic to a lot of non-experts. Lucas Duplan the founder was a Stanford CS student and probably had a lot of VCs thinking "next Mark Zuckerberg!!". Smash cut to September 2014, and the product they launch is a debit card for college students that allows users to amass rewards and share those rewards with friends via a mobile app. Pretty big letdown.

In the case of uBeam, they have a confident young female founder trying to tackle a very technical problem. She talks a great game and is able to wow the press and investors with a demo that is very impressive to a layman.

It's worth noting that despite Andreesen Horowitz's great reputation, it just so happens that they were one of Clinkle's investors as well and so that can't be used as evidence that all necessary due diligence has been done and the tech/physics all check out.