I'm confused as to why this is really a big problem. Sometimes, people really muck up replying inline, and it is somewhat harder to find their comments, vs. having their comments completely seperated from the previous message. Perhaps it depends on the class of user that you are serving, as well.
I do like replying inline when it comes to email conversations with one person. It's when things get too "deep" and you end up with layers of comments in comments with different people that things get too iffy. Perhaps this is why Google Wave was created (I really liked that product).
As for support, I am not an expert in that field, but I am guessing that support generally ends up with an in-depth conversation about a few specific topics.
I also guess if X people like replying inline and Y people like replying in comments, then any system that says "reply above this line" is ignoring those Y people. I have caught myself trying to reply inline when I was asked not to.
I worked in a M$-Shop for a long time. It was a huge problem there because Ms Outlook didn't do inline correctly. The inline text was in another color. And using a Linux Client you could only get the plaintext version without the color in it :( .
Basically I had to use a VM just to understand the mail correctly.
It's not the colour per se. Some email clients when not using plain text end up formatting your reply in the same style and colour as the quoted texted. The formatting may get lost on other email clients.
This is why I always use plain text so I get '>' infront of each line of quoted text.
The author seems to think they want to have a conversation with him. They don't. They essentially have sent him a form to fill out, and they want the answers together at the top because the answers are all they care about.
That's because you're not having a conversation, you're filling in fields in a form. You're lucky they let you use email instead of redirecting you to a web form that more rigidly enforces the method of interaction with them (which needs to die even more).
Not always true. I have had conversations with a lot of companies and they genuinely wanted to talk and help but the top posting kept messing up the flow.
There certainly are companies that don't want to engage in conversations but there are quite a few out there that do care.