This may apply with OS X apps, but with iOS apps it doesn't make sense. For $0.99 you have little to lose if you download my app and you hate it, but to make a dumbed down free version that will entice you to buy my paid app I have to redesign it. I have to think from a marketing perspective. What can I take out to make it painful enough for you to buy? Do I put in a nag screen? Do I put it on a timer? If I am going to do all that I might as well make the app free and put in iAds.
yeah, as you can see in the article, he's talking about the Mac App Store. For iOS i can agree with your view. It is absolutely fine, to sell a $0.99 App without any trial or free version. But for $9.99 or more, it is a pig in the poke situation.
Is it against app store policy to release a free app, then lock it down after 30 days (or some other time period) if they don't pay (purchase an in app payment or subscription)? That is a traditional "free trial" approach, but I don't think apple even let's you do it.