Speakers have a much more airy feel to them when compared to headphones. Yes, I have heard the HE90 (though rather briefly), but they still have a certain x-factor missing in them. They are great, definitely, but aren't perfect.
My experience with speakers is far more limited than that with headphones, but from whatever I have heard (even cheap 2.1 systems), speakers have that airy quality to them which make them sound very appealing. Still most speakers I have heard cannot match the resolution and detail which headphones can provide.
On a side note, what do you guys think of the Mordaunt Short MS914 pairing with the Marantz PM4001 and CD5001? It'll probably be my first speaker rig.