That's surprising to me, as a user. On Android I often search for apps, find the "free" one, read all the reviews and (if it has positive reviews) I seek out the "pro" version and buy that without ever having installed the "free" version. That is, I know the "free" version will have the top placement and the good user-feedback info so that's the one I can quickly get info about, but I skip the middle-step of installing the "free" one and move straight to the pay-up-front thing.
It's really because of Apple and their rules. Apple discourages Free and Pro versions of the same app (they may have loosened that up recently, but at one time, in an effort to combat app clutter and promote IAP, they would reject you). On iOS, there is no real way to try-and-buy without Freemium. At least in Android, and I think WP, you can get a refund within a certain time frame. Couple this with users generally seeking out free or super cheap apps and treating them as fairly disposable, just having a premium app for an upfront price, not being an established known brand, is basically a death wish.
Ah. Yes, WP actually has built-in support for offering both a "try" and "buy" version of each app, allowing two apps to coexist as the same entry... but in practice, most follow the "free" and "pro" naming-convention and offer two separate apps.
I hadn't realized that Apple's strict curating prevented these patterns.
You also can't return an app in iOS. If there is something grossly wrong you might be able to talk support into it, but in general that $5 purchase is final. I've heard that as a popular reason for the IAP model after people stopped buying apps after buying real duds for real money.
I guess my workflow is unusual.