For my money, the new iphone 4s has exceptional sound quality, but more over, it's smaller than anything else out there. Why? Because I have to have it with me at all times anyway, so even something 1/2 the size of the clip would be a lot more bulk.
I own the pico slim amp for my JH13s, because it's the best amp I've heard for them, desktop OR portable, and I own the JH13s because they sound better than any closed cans I've heard AND they have the added benefit of being easily portable.
But I agree with the point here, because often, despite having the pico slim, I don't even want to use it outside. Why? Not because it doesn't sound better. Just because the amount better that it does sound is easily dwarfed by the sounds and feelings of the outside world. When you're walking, your feet are going to be making a massive kinesthetic impact on your hearing, not to mention cars, other pedestrians, screaming kids, and so forth. Finally, even the tiny Pico Slim and the smallest LOD already adds a lot of added bulk. My iphone fits precisely in my pocket. Connected to a pico slim, it does not. the cable of the LOD can always get caught on things, whereas the cable running to the JH13s does not.
Maybe if I was going outside to some incredibly quiet place (is there one in NYC?) to listen to music, it might make sense, but for me, grabbing the Jh13s (since I already carry the iphone) is the utmost in simplicity, and for that, often takes the prize over an incremental boost in SQ.