Ignoring the initiation software (BIOS/UEFI), most of the laptops/computers can run completely free gnu/linux systems... Most probably wifi or bluetooth or discreet graphics wouldn't work. Sadly for majority of people wifi is more important than their freedom.
For my case, the bluetooth doesn't work, I just don't use bluetooth. RMS once had a laptop which he used without wifi. You just have to make these small sacrifices. :-)