Regarding the rear arms, the lower a-arm pivots on a tighter arc than does the upper arm, pushing the bottom point of the rear bearing carrier/upright outwards more than the top point during bump. This causes a negative camber gain, and counteracts the body roll while cornering to keep the tire contact patch flat. It appears that the lower a-arm connects to the upright using a double shear joint, which indicates that it locates the the upright, and therefore, the direction that the rear tire is pointing throughout the travel. From what I can tell in this pic, the relationship between the two a-arms will cause the rear wheel to toe outwards, while at the same time increasing the negative camber as it bumps. This will assure a car that over-steers into corners instead of under-steers, which makes sense because the last thing you want to give a novice driver is a car that under-steers. The consequences of losing control while cornering with this arrangement is that the rear of the car will most likely come around, backing you into the wall. Compare that to the front end pushing out, causing you to go head on into the wall. I'll take choice "A" anytime.The way the lower front mount appeared higher than the rear lower mount I dont know if it would get to the point of going forward, but if my eyes aren't deceiving me I assume Yamaha did it for a reason. The front reminds me of what Honda use do to on their 250R quads angling the front control arms up in front about 5% or so. They sure handled nice.
I believe you are already aware of what I am about to say, but I will include it anyhow for the benefit of those who aren't.
In the example of the front suspension on the 250R quads, the inclining upper arm would be for the purpose of creating caster gain as the suspension bumps. Positive caster is what causes your steering wheel to return to center when you let go of it after a turn. It is created in a front suspension by positioning the top ball joint rearwards of the bottom ball joint, relative to the direction of travel of the car. The effects of negative caster can be felt while backing up, where letting go of the steering wheel only allows the tires to steer sharper. Too much static caster set in a front suspension makes the steering feel heavy, and scrubs excessively while turning, causing excessive wear to tires and components. Just look at any old Ford twin I-beam pick up truck with its lofty setting of 5-8 degrees of positive static caster at ride height when turning the tires, and you can see the results of excessive caster settings. Not only is it seen through the wear pattern on the tread of the tire (an uneven wearing of the tread, otherwise known as "cupping"), but the inside tire literally lifts that corner of the truck off the ground by nearly an inch or so when the wheels are turned full lock. This is due to the massive caster. But, because caster inhibits the "return to center" characteristics of the front end, we need it for stability. With parallel mounted upper and lower arms, when the front end "dives" under braking, it causes the steering axis inclination (an imaginary line drawn in between the center of the top and bottom ball joints, referred to as SAI in the automotive industry) to rotate forward, negating any positive caster there was dialed in at ride height. If the static setting is minimal, the caster will become negative, causing the front end to wander more than one would like under braking. Inclining the upper a-arm pivot axis towards the front of the vehicle simply moves the upper ball joint rearwards as the suspension bumps, while the level bottom arm keeps that ball joint in location (fore and aft speaking). This causes the caster in the front to remain positive throughout the wheel travel with out excessive static settings. Positioning the upper arm as described above is also referred to as "anti-dive" geometry, and is built into most any modern day automobile, and all properly designed race cars.
I'm sure glad I didn't have to give that explanation out loud. I would have confused the hell out of me and you!