Machine Options in CAM Software ?

While I'm waiting to buy my mill for the retrofit project I have been
playing around with different software for the CAD and CAM part. Why
do the different CAM softwares ask for what type (Fidal, Faunc, etc)
of machine? I thought G code was somewhat universal for CNC? Is it
because not all machines use all G codes?
Also, is the G code converted into step and directions signals in the
NC software? Thanks for any clarifications!

Mark