Thats not entirely true, that means that the computer has no OS. A computer with no OS is pretty worthless to me in my opinion. Same with the heart, whats the point of a heart if you have no memories/feelings. Thats why the nobodies have no feelings, cause they have no heart. They retained their memories because they had a heart at one point in their life. He seems totally devoid of emotion. But Xehanort is a special case, he's the only heartless shown so far to have a human body. Also it's stated that he started to create artifical heartless and branding them with a crest. The natural heartless are the shadows. The created heartless are the ones with the crest. What if he created a heartless and found a way to bond his heart to it, thus destroying his original body, and making the nobody Xemnas.
Throwing out more whack ideas
...where to start...where to start...
memeories and fellings are different, he lsot his old memories, so now hes making new ones, such as,w aht is darkness, who is riku.
nobodies do ahve feelings, when you lose ur heart, the soul takes over
the reason xehanort is different is becuase he had hidden memories, so thsoes memories kept him from being completly heartless, its complicated to go into the whole story.
xehanort himself said that he "cast off his body and plunged into darkness" so he didnt fuuse with a heartless, he plunged into darkness, and nobodies are created when the heart cast off the fleash, weither willingly or not, and thats why xemnas was made