Why would they want to remove the ability to do screen captures?
The resources that screen capture apps need in order to take a snapshot of the screen are outside of what standard user privileges give which is why normally, root access is needed.
The reason that I said that it'll probably be patched is because it's probably a side effect (albeit a nice one) to other security issues that I remember reading about regarding the EVO 4G (such as the reasons that root access was accomplished so quickly and easily compared to other devices). And if/when the EVO receives a patched update, I would assume that the trickle-down effect would close the screenshot ability. Not intentionally though since it was probably never meant to be intentionally opened in the first place.
That is just strictly opinion and random thought on my part. Anyone is more than welcome to prove me fully wrong. In fact, I would like that.