They may have thought through all of your questions but decided not to have firm answers right now in order to validate the idea, and not the technology.
The problem I have with the lean startup movement is how easily it is to get derailed before you ever even begin. For example, the lean startup movement suggests an initial qualitative approach to testing your assumptions, achieved by talking to a small number of people in your target market. But that assumes you know who your target market will be, that you know who the early adopters in that market will be, and that you're asking the right questions. If you get any of those wrong, poof! You'll believe your assumption wrong and your idea invalidated even those it hasn't been.
The founders of Jarvis may have done their homework prior to releasing a product. They may have concluded that there was a real pain point that their service could solve. But what research should they have done to realize that their target market wouldn't be interested unless they had a legal page? Or demonstrations? The problem with trying to go with the absolute MVP is that it's way too easy to go too minimal.
The lean startup methodology will work best for ideas that solve massive pain points. With a massive pain point, it won't matter if you're talking to someone that is normally an early adopter or someone that normally trails behind. It won't matter if you have a poor design, a minimal feature set, and no legal page. But for anything else, it's just entirely too easy for your target market to dismiss you and for you to summarily dismiss your idea.
Absolutely agree with you and I wish the folks that teach lean would emphasize this more.
For every successful company, there are probably multiple teams that tried to test the same general idea only to conclude that it won't work.
Overall, I think lean start up movement does a great job of taking credit when it works out while not delving enough into all the people who gave up because the idea didn't validate itself according to the lean process...and yet another company with a similar idea made it work.
So, one problem with lean is that you're actually testing two variables: the idea and the execution. When people don't convert, is it the idea, the copy, the design, something else? It may be that you just need to iterate on your copy/conversion funnel, etc. a dozen times. But, lean de-emphasizes the implementation; encouraging you to instead view the feedback as primarily relevant to your idea, and so move on in the face of low conversions.
That's a bit of a "no true scotsman", isn't it?
Certainly it must be true that encouraging people to belt out a "minimum viable product" results in the launch of something half-baked and unviable at least slightly more often than if the advice hadn't been taken. That doesn't invalidate the lean startup concept, it just illustrates a potential tradeoff... and there's always a tradeoff.
I'm remembering this for the next question my boss asks me...