They really don't. But the article is misleading, because the 'long copy' example provided, the highrise teaser page, is not an example of long copy. It's a well formatted bunch of meaningful information, strategically designed and placed carefully (flow) that keeps enticing users to read more of it.
It's a well documented fact that people DO NOT read long boring paragraphs. They DO, however, read highly entertaining webpages with a fairly big copy so as long as it breathes and attracts them.
So to wrap up, yes write more than a sentence, no don't write a book. Instead, carefully craft sentences to entice potential customers to turn into real future customers.
It may be true that people do not read long boring paragraphs, but I'd bet the research to which you're referring is not addressing ad copy. If it is, I'd like to see it. It is in fact well documented that long form sales letter DO convert better than short copy in many situations.
Read here for context of the example used: http://37signals.com/svn/posts/2977-behind-the-scenes-highri...
If you are offering a free product, then short copy is best. Users will trade trying to read what your product does to just using it instead.
Sure there are people doing it wrong, but done correctly its a powerful tool that raises the odds that your startup will become a success.
The landing page trend is just for early adopters, I would venture a guess that it has little to no impact on the success of a startup.
I think the OP's main point is that instead of having a landing page you should be concentrating on product/market fit by describing the product. I think startups with these coming soon pages are already doing that, just not on their public website.
It's (a) a placeholder, (b) incentive for me to stick to a launch date, and (c) it might, just maybe, collect a couple of email addresses.
I'm under no illusions that it's going to generate any sort of buzz, become vital, etc. It' just better than a 404 or something like http://www.google.com/search?hl=en&gbv=2&tbm=isch... :-)
