Yes, what you said is exactly correct. The reason they are 6+2 in your psu is because some cards need 6 or 8 or 6+6 or 8+6 or 8+8 and it can accommodate all of them.
I heard that the 6+2 pin connector provides lower power than the 8 pin connector, is that true? or is it effect my GPU? (kinda like make the GPU run...weak?)