What advantages do ridge cap shingles have over modified 3-tab shingles?
Less chance of cracking
Standard shingles are a bit thinner than ridge cap shingles, and can crack or tear when folded over the ridge.  Ridge cap shingles are thicker and come pre-bent, so there is less chance of cracking.
Better adhesion
Most ridge cap shingles have an extra dollop of adhesive near the end of the shingle, to help hold it to the shingle below. This helps to prevent blow off in heavy winds.
Thicker nailing surface
Ridge cap shingles have a thicker nailing area, which helps prevent tearing near nail holes.
No extra prep
Since ridge cap shingles are designed specifically for the ridge, there is not preparation required. Just open the box, and start slapping them on.