Why use lossless even when you can't hear the difference?
Modern lossy encoders, including good old MP3 using LAME VBR settings like V2/V0, are very very good. So good that few people can tell the difference when listening carefully on good equipment. Evidence from blind testing on forums like Hydrogenaudio.org backs that up. On a portable player used when jogging or traveling by plane/train, you just aren't going to notice any subtle loss of quality.
This is very true as long as your MP3 player equalizer is not used.
Otherwise anybody will hear a difference instantly (no blind testing needed here).
So it all depends on your settings and your headphones.
All should be "frequency flat" (amplitude) if you shall not hear any difference.
This is also the way the producer intended you should listen to it. His mixing and recording equipment should be really audiophile (=frequency flat) amongst other things.
In reality headphones (mostly cheap ones) often limit bass response (that you will boost for compensation on your equalizer).
And in this case (often in real life) the sound will also be different than what the producer intended regardless if it is lossless or lossy encoded.
But it will sound worser with lossy encoding as a result of the (lossy) psychoacoustic model used to to make the file smaller.
Then (in such cases) you will hear a different sound using lossless compared to lossy encoded music.
With small earphones it will particularly be harder to get good bass response so then it can be more noticeable although you use expensive "good" earphones.
Nobody at Hydrogenaudio has ever said anything else as far as I know.
So in simple theory you are right but it actually depends on your equipment too.
In fact this is one reason it is quite difficult to build very good speakers because the elements and the resonance box (speaker box) will not be frequency flat. Because of that speakers use several elements and filters (for flatter frequency response) but although this is done it will destroy the sound quality to some extent because the end result is still not perfect flat response (although hopefully close to).
The engineering behind this (box, element, filter design) is thus relatively demanding to do, to please audio enthusiasts. The speaker position in the room and the room dimensions and furniture also matter for resonance. That is why room compensation algorithms are used sometimes too. With clever design good and not too expensive designs are possible (within some limits).
With headphones it is not equally hard to get good quality per $ because the produced sound does not need to be so loud and the distance to your ear will always be the same regardless of your position (in the room).
Edit: In short when you try to compensate for "bad" gear like small PC speakers with your equalizer you will hear a difference. Otherwise maybe not.