Great points, your article was spot on. No, definitely that's not the main issue, although it is one. You can't keep reinforcing why the user is signing up throughout the process the same way you can on the web. All mobile sign-up screens pretty much look the same and I see a lot of users look at it and just delete the app, or delay until later at which point they forget why they downloaded it. And even when they get past it, if they see something else they perceive as a "this is going to take a while" moment, they are going to leave and delete your app. On the web, the time to signup and get use from your app is faster and perceived as faster so I think given a choice between the two, more users would do it on the web.
Most landing pages on the web look the same too. The best signup flows I've seen or created don't need to continually re-enforce why the user is signing up, they just need to lead the user down a logical path towards fulfilling the original value proposition, the reason they typed their password into the App Store and took the time to download your app in the first place.
If the user is bouncing because they think "this is going to take a while" then you either don't have a strong enough value proposition or you're making the user think too hard. Most things can be reduced to simple, one-decision steps, and when you do that things will generally convert better for you.
