I believe it has something to do with the contractual way the Fare is carved up amongst the carriers.

From this forum I have come to understand that the transcontinental carriers get the largest slices of the xONEx 'pie'. More here: Airline compensation for one world explorer.

I would guess any contraced formula is based on several factors including a minimum requirement of having ASIA<->N/A, N/A<->EUR and EUR-ASIA transcontinental segments. To allow a defined a N/A-ASIA segment as such would invalidate the contracts. To get around this, the airlines have agreed an ORD<>DEL segment be defined as two transcontinentals, N/A<>EUR & EUR<>ASIA.