I'm not sure why purrin's getting criticism for calling the LCD2 mid-fi. That's exactly where I'd put it, too. I think most of us break categories up into 3s (low/mid/high) and 5s (low/lower-mid/mid/upper-mid/high) to file our experiences and perceptions. Most of us probably have different weightings on what constitutes each of those categories. I place detail and resolution near the top of my list, so the only headphones I've heard that I'd call high-end are the SR007, SR009, and HE90. From my experience, going from each of those headphones is a sidegrade, where you end up getting some things and losing others, but they all net fairly even to me. A lot of people factor price into their categorizations.
In the mid-fi category are the LCD2, RS1i, HE500, etc., with the HE-6 and LCD3 (maybe) in upper-mid-fi. Low-fi compromises the majority of headphones on the market.
Just categorize things however makes you happy and fits your world view. This hobby isn't exactly objective.