Mellotronists

With a sampler, you can press a key and sound comes out. You can even 
play with the envelope and get different attacks, every note with 
exactly the same attack. With a Mellotron, you can press a key in many 
different ways and change the attack. You can also change the sound by 
changing the pressure on the key while a note is playing. It isn't 
just the sound, it's the feel. There's no way a sampler can feel like 
a Mellotron, so there's no way you can put the same feeling into the 
music you're playing.

On the other hand, Mellotrons are expensive and not everyone can 
afford one. But a multi-function sample keyboard loaded with decent 
Tron samples would be more useful than the Memotron, which can do only 
one thing; and it wouldn't necessarily be more expensive.