Let me try to explain why a target curve, as opposed to flat, makes no sense, and why this myth has come about. Understanding one concept is crucial: we 'hear past the room'.
Quoting Dr. Toole:
Humans evolved while listening in reflective spaces, and are comfortable listening in them. In fact, it is now widely recognized that we perceptually "stream" the sound of the room as separate from the sound of the sources - that is what happens in live performances. A Steinway is a Steinway; only the hall changes. ...a good loudspeaker is a good loudspeaker, and its virtues are appreciated in a wide variety of rooms
The only question is whether you believe it or not. If you believe it, then it follows that the 'target curve' makes no sense. Not only is the concept of a 'target curve' an inversion of what is in reality a passive correlation, but it also has no relevance to headphones - it is a double absurdity for headphones.
Where this myth comes from is this: you, the listener, are able to separate the sound of the room from the source (including the speaker as source) as described above. This is an evolved ability, crucial for recognising and locating the sources of sounds in arbitrary environments. You hear the source as though there is no room; you hear the room as separate 'ambience'.
A measurement mic and laptop has no such ability: it simply measures the amount of 'frequency response matter' that passes through a time window during the measurement, including the direct sound from the speaker and the reflections. The natural effect of reflections in a real room is to attenuate higher frequencies more than lower, so the measurement of a perfectly flat 'ideal' speaker in a room shows a droop at high frequencies.
But this is not what you are hearing. You are hearing the speaker as though there is no room, and "streaming" the room separately.
So why do people seem to prefer a target frequency response? The answer is: they don't. What they prefer is a flat speaker. Putting it in a real room changes the in-room frequency response measurement, but not their perception of the speaker. Most good speakers in average rooms will tend to produce similar in-room frequency response curves, hence what appears to be a 'preference' for a particular frequency response. But this is the wrong way of thinking about it. And it does not follow that reproducing that in-room curve using EQ in a different room will sound the same to the listener. It won't. You will have modified the speaker's sound by changing its EQ. The listener will then hear the speaker as arbitrarily modified regardless of the room.
And it certainly won't sound the same in headphones. With headphones there is no room, so they should be adjusted to flat. There is, however, the possibility that if some recording studios are making the same mistake (believing the target curve myth), then their recordings become skewed for listening with the 'target curve' - what Dr. Toole calls 'the circle of confusion'. There is no answer to that conundrum.
Sadly, even if all engineers used headphones adjusted to the same target curve, and you did the same, it still wouldn't produce a perfect result. If they mixed the recording followed by a perfect EQ inversion of the mistaken 'target curve', the result would be perfect. But in reality they will probably assume they are hearing perfection (the target curve is 'official' after all) and simply adjust faders and adjust EQ of individual channels ad hoc, meaning that they get it 'about right', but you, and they, will still be hearing the 'target curve' smeared over the top of those flat and arbitrarily EQ'ed sources. It's a mess.
Ideally, all headphones should be adjusted to flat.