Doing this also gives the developers the option to introduce paid updates in the future, which is potentially good or bad.
There is also no reason the developer can't link to the paid version direct from the app - no heed for hunting.
I don't mind them charging in-app for features in principle. but I found that the free version wasn't enough for me to draw anything serious so it didn't really let me try out the app.
I think it would have been better to go with a fully featured free version with say, just one notebook with limited pages. That way users could use the app fully, and upgrade if they used it enough to need more capacity.
Wow...UX in systems with hidden file-system is so awesome.
In general, your argument about a subset of products is reasonable. In a drawing app when you have to buy individual brushes it's scummy.
I feel it's actually more respectful of the user's time to let them figure out whether the app will work for them for free, rather than forcing them to commit to a purchase of something that may not in the end be suitable for their needs.
(insert discussion about being able to return apps for a refund here)