The whole point of the lean startup approach is to posit that the "business school approach" is wrong, exactly because you don't know all this stuff ahead of time, and that "business plans" are an outdated idea.
And if what you're doing is a truly novel product, then you almost certainly don't. If you're using the "fast follower" strategy to be the nth company doing a product in a certain space, then sure.
OTOH, even Steve Blank says that there are certain areas where you don't need to do Customer Discovery / Customer Development... like, if you're creating a cure for cancer, it's pretty much all engineering. If you build it (and it works) they will come. But I think that kind of scenario is the exception, not the rule.
A startup is "an organization dedicated to creating something new under conditions of extreme uncertainty" (quoting the insider cover of Eric Reis's The Lean Startup). If there isn't extreme uncertainty, then it isn't a great fit as an overall strategy.
On the other hand, the LS counterpoint would be that you'll miss considerable insights if you rely on existing knowledge/research (Ford's classic "If I asked people what they wanted, they would have asked for a faster horse" quote....)
EDIT: i guess my point is, engineering isn't cheap either. Shouldn't be OK spending that money ahead of product fit either.