TS_Hawk, options for giving 'Mechs large turrets and center torso cockpits have been in the game since about MaxTech, which I think is a c2000 publication.
If you look in MaxTech or, more recently, Tactical Operations, you'll find several turret options for 'Mechs. A typical one for quads is to designate one of their side torsos to be a turret. This gives you a well-armored turret. There are several other turret options, too.
Center Torso cockpits were introduced in the Unbound scenario pack and are also available in Tactical Operations. You can put your MechWarrior behind the heavy armor of the center torso if you want, but it's a death trap. From the front, 7 times as many shots hit the center torso as the head (rolls of 2 and 7 on the hit location chart account for 7 of 36 possible 2d6 combinations, while a 12 - for the head - only accounts for 1 in 36). Further, all damage transfer paths lead to the center torso, so accumulating damage will only increase the risk to the MechWarrior. While a head-mounted cockpit is more vulnerable to one-hit decapitation by big guns, a center torso cockpit has proportionally less armor when averaged over many shots.
when I look at the mini's
During reviewing an upcoming publication, much higher priority is given to the rules and fluff before falling back to artwork. Artists - be they sketching a 'Mech or sculpting it - take liberties to make something look cool rather than how the game works. I'd suggest starting with the game rules and asking about the art rather than vice versa.
it just kind of strikes me as why did FASA do it this way?
Because it was a convenience to use a single, standard set of rules for the cockpit - pages of extra rules are needed to address alternate cockpits.
And because it is fun to blow the head off a 'Mech, be it a distinct human-like head or just part of the torso.