What is the difference between a low end and a high end rework station, and why pay for a higher end station?
Exterior similarities don't really mean that they're assembled to the same spec, with the same quality of components, at the same level of quality control.  When dealing with tools, a lot of them will look the same or similar.  Functionality is key with a tool, and there's going to be a general similarity in controls and layout with tools offering the same or similar functionality.

At home I use a Hakko digital soldering station, while at work we use Weller units.  Both are similar quality and price (around $100), and both share a lot of control layout similarities to my old Radio Shack iron that was $40 and burned out in a year.  Certain controls are necessary, and they're going to have similar positions because that makes the most sense for the user.

The first two rework stations are probably made by the same parent company and are identical in circuit and chassis design.  Component choice and quality control might be better on the Kendal, which is why it sells for more.  It might also just be marketing, as some people will pay more for a domestic-sounding name, believing it to also be better quality.

The Aoyue looks like it comes with more stuff, which might be enough to justify the higher price without being a better quality unit.  It's also advertising additional features, which in marketing commands a higher price.

There's also the fact that companies might be imitating other, better-known units to ride on their coattails and grab sales from people who thought they were buying the brand-name unit.

TL;DR there are several reasons why units might look the same or similar, but that doesn't necessarily mean they're all the same underneath.  Only you can decide if it's worth it to buy the more expensive unit.