Based on the specs the only substantial difference is the minor difference in size.
The only reason I can think of is the LCD panel availability. LCD panels comes from many, many difference sources. Perhaps when not enough 23.6" LCD panels are available, the manufacture monitors with the 24" LCD panel. Idle production lines means you are not going to make any money so the manufacturing plants may switch between the two types of monitors to maintain continuous production.
That may not be true, but it's the only reason I can think of.