Whoa.
Lots of BS AND good info put forth above. Let's try and sort it out.
First, a shorter barrel does not necessarily mean more inaccurate than a longer barrel. A longer barrel will impart more Muzzle Velocity (MV) and will mean less drop over the the same distance traveled. This can make range estimation less of an issue with longer barrels, hence greater velocity, for the same round fired through two barrels of different lengths. This assumes both bullets are stabilized appropriatly.
Second, slow rounds ar NOT inherently more inaccurate or are those with greater verticle movement over their trajectory (high arcing bullets). I was in the artillery and we fire projectiles up into the air at angles higher than 45 degrees. They could be placed with in yards of each other 10 miles away. Consistency from round to round is what makes for accuracy.
Third, the gyroscopic effect (why a top when spinning fast doesn't fall over) is the force that stabilizes a bullet. Not enough spin will cause it to wobble or yaw. FOR LONG RANGES (over three hundred yards) if the bullet begins to fall at a rate that lets the bottom of the bullet develope pressure (the direction of travel is down some what but the bullet stays horizontal) the bullet will be over stabilized and it will start to wander in the direction opposite to the direction the bottom is rotating. This is how a curve ball moves. Again if it's consistent, the lateral distance will be the same from round to round and it will not be more inaccurate, it will just move to the left or right (depending on the direction of spin). It will move more at longer distances. It is not uncommon in high power shooting to have to add a click or two of windage for the 600 yard range on perfectly calm days. If the bullet is stabilized correctly, the bullet will tilt forward to keep the nose pointed in the direction of travel thus minimizing the affect.
There is a lot of good info in the ammo oricle and over at the compitition forums.