Correct me if I'm wrong (I sincerely mean that), but...the reason why they are being treated differently is because Unity's offer is not as good for the small developer and is presented in a much more dishonest manner.

• Unity's is "free" except if you want to do certain things they advertise as primary features where you'll have to pay a large sum. So, it's a bait and switch. They call it free when, to many people, it's not. Second, there is a pretty good indication that they are trying to "shame" developers out of the free version with the "personal edition" message. So, Unity's "free" feels underhanded. Their website starts by listing ALL features and then saying, "Whether you download Unity 5 Personal Edition for free, or buy or subscribe to Unity 5 Professional Edition, you pay no royalties and the content you create as a Unity user is yours." It's not until you click "get unity" that they show you that all of that stuff they advertised is not available to you and start breaking it down. There are phrases on this page like "limitations apply" which you have to click to reveal additional information. The whole thing is a bait and switch, which customers generally don't respect.
• Meanwhile, for somebody who makes less than $12k per year on games, Unreal is free and its price scales with your success so you should never have to worry about it not being affordable. For that "free" price you get the full advertised product rather than a cut down version. Their website is not at all deceiving (because neither is their offer). It says in large font, "Use for free." and then "5% when you ship.". The "fine" print below that is 16pt and actually does the opposite of normal fine print by letting you know scenarios where you don't have to pay the 5% ("The 5% royalty starts after the first $3,000 of revenue per product per quarter. Pay no royalty for film projects, contracting and consulting projects such as architecture, simulation and visualization."). So, Unreal seems more honest, straightforward and respectful with their customer.