I disagree... Some put more work in it than others, the results may not be up to the amount of work spent, and one might consider the price difference to not be worth it, but that's not the matter here imo.
eg:
- shapes vary largely (2 donuts are not always the same, the air distribution can be quite different)
- inflators are not all the same, nor is their position. eg x-deep and tecline have done some more work on the placement of those. Scubapro has a "balanced" inflator, ...
- bungee'd wings of death (OMS) vs bungee'd wings of life vs non-bungee'd wings of redemption
etc.
There might also be more subtle differences that one doesn't notice immediately. Add to that that you might get some service from one, and none from the other, ...
So yeah, there's sometimes a reason for a difference in price. Not that I could necessarily tell a large difference in all models suggested, just saying that there might be.