matte black vs. photo black

Can someone tell me why, in my Epson printers, the only ink I have to  
change when I change the finish of my media is my black?

Why don't I have to change all the others, too?

The sky doesn't fall if I print with matte ink on pearl paper so why  
do they say I'm supposed to?

Thanks,

Lea
(who is puzzled)

babies. they're what i do.
www.leamurphy.com