A conspiracy theory (well, my definition) is rejecting the mostly likely scenario for one that seems more logical based on detailed analysis and the expectation that everything must be more complicated than it first looks. The most likely scenario here is that Sprint simply wasn't willing to subsidize the phone enough to get it to $199 because the price of the device from Samsung was too high. Instead of assuming that was the case, most here are assuming it has something to do with EVO cannibalization, even though A) I've provided many reasons why that's not true above, and oh yeah, B) SAMSUNG WOULD BE PISSED!
Imagine you're Samsung. You spend all this time working on a device for Sprint that is different from all the other devices in the entire US, and then Sprint tells you, "Hey, we don't want people to have your stupid device, we want them to have this other one from your competitor, so even though the price from you is the same as this other device, and the costs to us are exactly the same regardless of which phone the customer buys, we're going to subsidize this less than we normally would because we want to help out your competitor." Samsung would obviously be furious. Device pricing cannot be done that way, and it is not done that way.
I think you can all agree that Sprint can't afford to anger a manufacturer that.