Two bars with the same number of drive links won't necessarily be the same working length. The shape of the bar is what is different. A circle and an oval can have the same circumference, and the oval will be longer in one dimension than the circle. You can make a 24" 84DL bar into a 25" 84DL bar simply by changing the shape. Most of the standard length OEM bars for a given chain pitch stick with a standard length chain for the simple reason that it makes it much easier for the customer to buy loops that will fit, regardless of brand. If Stihl made all of their bars one drive link different (for a given pitch and bar length) just to get you to buy their chains and bars, customers would revolt.
Aftermarket, high quality bars are a bit different. For a given length bar and pitch, the engineers may be designing the shape of the bar for optimum performance, and to hell with standard drive link count on the chain. If you're after an expensive, high performance bar you are less likely to give a rat's ass if you've got to have the loops made to an oddball drive link count (or do it yourself). It's annoying, but Cannon, Sugihara and Tsumara all do it on some of their bars. Sometimes it is obvious why they do it, as in specialty bars like carving bars, racing bars, etc. because sometimes the shape is more important to them than whether an OEM loop will fit it.
I agree, though, it's confusing and annoying for the customer... especially if buying a factory loop off the shelf is important to you.