I think that there a few different meaning behind it when people say they hope it's due to PTSD, or say that the PTSD is what is causing the situation.
In my case, I don't necessarily hope it's PTSD or "please tell me it's PTSD"... I would just like to know if something is because of that, or not. If it is, it changes how I view the situation. I understand that it's not my boyfriend's fault that he has PTSD, and he is trying very very hard to get past it. But, because we are all human, sometimes he slips up. It helps put things into perspective for me -- he isn't doing this on purpose, he may not even realize how it's coming across.. Maybe I should be more compassionate and understanding than annoyed and hurt. If he says something or does something and he says PTSD wasn't a factor, that also adjusts how I react (but even then, I am still usually more compassionate than I would be to someone else because I realize that even if he isn't aware of it, PTSD floats along into other aspects of his life and may be affecting it unintentionally).
I have multiple chronic illnesses, none of which are PTSD, but they affect me every second of my life. So I understand what you guys are saying about how you aren't PTSD, you aren't your disease. I get that. I'm not my disease, either. But at the same time, I have diseases that affect my functioning, same as your PTSD. Isn't it just respectful and nice for people to realize that and adjust their ways? Perhaps you see it as a form of discrimination because you have PTSD or babying you, or treating you differently, and I understand that because I don't like to be reminded of my disease all the time, either. But most of the time people do it with good intentions, to try to work with you or make your life better (or so they think). Just a thought.
On the flip side, I see that a lot of people on here hope that it's PTSD because that is a convenient excuse that can be used to cover up bad behavior. At the root of who he is, I love my boyfriend completely. Sure, sometimes he does things that piss me off, but I like the core person that he is, his values, the way he treats people, etc. It seems like some people on here are with people who let their PTSD overrule them and treat people extremely badly, and the supporter says "oh it's just PTSD" instead of "wow, this person is extremely abusive on a consistent basis. I need to get away from this."
I think that mostly, we supporters tend to fall into one of the two categories... wanting to know if it's PTSD so they can understand better, and wanting to think it's PTSD to live in denial more. That's my opinion from reading this forum, at least =)