Quote Originally Posted by Silfir View Post
You have to deviate from the rules just to check for lethal damage as a state-based action.
No, you don't, because you're not checking for lethal damage as an SBA until after the creature has already lost indestructible as part of its static ability. It remains indestructible as long as it doesn't have lethal damage marked on it [CR 604.1, 611.3a], then the static ability says "Hey, you! You're not indestructible any more!" Then, once it no longer has indestructible, the SBA checks next time a player would gain priority. It's the same way that trample checks for lethal damage on indestructible creatures.

Checking the rules and the one relevant example more carefully, another way of wording it is "~ can't be destroyed by effects (It can only be destroyed by lethal damage or deathtouch damage)" or "~ can only be destroyed by damage." These are probably more succinct anyway.