There is only one clipboard. plus an additional text buffer.
As a multi system user with only one k/m input (windows/red hat), I love the differentiated buffer capability. It allows discrete usage of cntl x/c/v across systems and STILL allows me to manipulate c/p actions while multitasking.
There are lots of buffers in X, actually, it's just that only 2 are most commonly used. There're PRIMARY, SECONDARY and CLIPBOARD selections, and long-obsolete (but still accidentally used to implement cut/yank rings - a feature long forgotten by many) 8 cut buffers (CUT_BUFFER0 to CUT_BUFFER7).
As a multi system user with only one k/m input (windows/red hat), I love the differentiated buffer capability. It allows discrete usage of cntl x/c/v across systems and STILL allows me to manipulate c/p actions while multitasking.