You only normally see seams sewn with regular zig zag when the sailmaker
doesn't have a big capacity 3 step zig zag machine. This is also the reason why it is 4 rows, as if they used 3 step zig zag only 3 rows would be required.
Regular zig zag is normally used for UV strips because it is much faster to un-pick to replace the UV strip.
Triple stitched seams is a regular request by cruisers although in a lot of cases only 2 rows are required, it depends on the sail size and type of boat. It is about eliminating creep in the seam not about the life of the seam. If the thread is badly UV damaged it is going to let go, doesn't really matter if its 2 rows or 3.
Colored thread is a good idea as you can more easily notice when the thread is damaged or destroyed by UV