I think you're underestimating the number of people who go in to buy an iPad and gravitate to the Pro because it looks the coolest and sounds like a luxury thing. For those people, who are likely just going to use it for web browsing and streaming videos, the cheapest configuration is the only one they care about.

That type of buyer is a very significant % of sales for iPad pros. Despite the marketing, there are really not that many people (as a % of sales) that will be pushing these iPad's anywhere even remotely close to their computational/storage/spec limits.