I don't think we'll have to worry about scratching the lens so much. Have a look at pictures 16 & 18 in the Engadget gallery (no way to direct link to them):
Sprint HTC EVO 4G LTE hands-on - Engadget Galleries
In #16 you can see a small gap between the aluminum ring and the lens, and in #18 you see that the alu ring comes off with the plastic case part. Looks to me like this will provide some much needed protection for the lens. Sure, you'll still be able to scratch it, but it'll be a lot harder.
Sprint HTC EVO 4G LTE hands-on - Engadget Galleries
In #16 you can see a small gap between the aluminum ring and the lens, and in #18 you see that the alu ring comes off with the plastic case part. Looks to me like this will provide some much needed protection for the lens. Sure, you'll still be able to scratch it, but it'll be a lot harder.