Quite frankly, if I didn't recognise MacDawg from MR, I'd also take anything he says with a grain of salt. It's the internet, and he may not post here often enough for me to become familiar with him. Seems OK with me.
And yes, phone cases can degrade either mobile signal, or WiFi, and it doesn't need to be made of metal or anything for this to happen.That will cause some loss of battery life. I'm not sure about 40%, but if you use your phone for internet often enough, a case could greatly increase the battery consumption of the radio by 50%. Sure, that's just the radio, and not things like the screen, so it wouldn't matter that much. I'd believe 20% though if you're an avid Tumblr pjorn freak like me.
I barely use my phone for talking, so it's just animated gifs, spamming forums, etc.
i'm no engineer but I would seriously doubt that the Apple leather case would cause a 20% drop in battery life and 40%-50% NO WAY that just crazy. I don't think Apple would release a iPhone case that would do something like that. I just tested it and my signal strength is -110 with and without the case on so the lose was 0.
All that said I did have a Spigen case with a metal rim and it killed my WiFi signal.
For anyone wonder here is how you can check for real and not just assume. That doesn't show WiFi though so maybe its killing your WiFi but I doubt it.
http://www.cnet.com/how-to/force-iphone-to-show-numerical-value-for-signal-strength/
