I gather that you read the thread, so I won't go point by point and explain the reasonableness of his responses to the issue. I will -however- link to the Github issues that I remember that contain relevant discussion. [0] (Issues 127 and 281 are particularly relevant. 282 is included for the folks who don't understand that Signal for Android is distributed under the terms of the GPLv3.)
Moxie cares about providing solid, functional, easy-to-use, as-idiot-proof-as-possible communication encryption software. His target audience is everyone, not just the technically skilled. To that end, he wishes to make it very difficult for non-technical users to get Signal from a source that is substantially less secure than the Google Play App Store.
Anyone is free to download the source and build and sign their own binary. If you're technical enough to do this, you're presumed to be technical enough to understand the risks you're taking by doing this. For everyone who is not sufficiently knowledgeable to build from source, any binary package distribution mechanism needs to be at least as secure as Google's, and provide the additional features mentioned in Issue 281.
Also notice that Moxie supports the effort to replace use of GCM with Websockets. [1] Google does security well, but Moxie is neither beholden to them, nor is he opposed to equally secure and capable replacements to the services that Google provides.
Whisper Systems is carefully doing excellent work with Signal. Software like this is a great benefit to society.
[0] https://github.com/WhisperSystems/Signal-Android/issues/127 https://github.com/WhisperSystems/Signal-Android/issues/281 https://github.com/WhisperSystems/Signal-Android/issues/282
[1] https://github.com/WhisperSystems/Signal-Android/issues/1000