Never heard the term "orbital" for a jigsaw, but i have a Makita with pendulum action and what sounds like the same blade fitting arrangement. The blade is held snug against the roller, but not with great force.

A fence with a jigsaw is a nightmare and i would never use one. The blades are flexible and so if you force a straight line cut with a fence, the cut may remain straight on the upper surface, but the blade will tend to depart from perpendicular to the surface (i.e. a slanted cut). This doesn't happen during freehand cutting because you are constantly correcting the cut direction (i.e. hunting, albeit within a very narrow range of movement, if you're good at it), rather than forcing it.

A jigsaw is not a tool for cutting a perfect straight edge. It is for curved and awkward shapes, or for making an approximate straight cut (can be made perfect using a router or other tool, afterwards).

Terry.