The difference is that the quick-reply box would be grayed-out until you hit the "quick reply" icon on a post. Once you do that, you should be moved automatically to the now enabled quick reply section so you can type your message in and then enable the "Quote message in reply?" option if so desired.
In all, I would imagine people would like the way it currently is better... but to me, it helps me keep a better routine, since I like to quote the messages I'm replying to, and right now I often forget to hit the "Quote message in reply" since it's grayed out by default regardless if you being able to type in the Quick Reply text box or not. So if we do the click thing, the text box AND the option to quote the message would be enabled at the same time, so in that regard it helps me personally quite a bit in not overlooking some of the options I use.
I don't think we even used to have a quick-reply icon. I think you simply hit on "Reply" and it would automatically enable the quick-reply text box for you to type in. That's if I remeber correctly.
