Abrogation of verses 10 feedings of baby to make foster relationship to 5

Verses of the Quran can be abrogated. But one stands out, the abrogation of 10 sucklings of a baby to 5 sucklings to develop foster relationships. Why? Seems inconsistent. What's the big difference between 10 and 5? Was 10 a mistake? > 'A'isha (Allah be pleased with her) reported that it had been revealed > in the Holy Qur'an that ten clear sucklings make the marriage > unlawful, then it was abrogated (and substituted) by five sucklings > and Allah's apostle (may peace be upon him) died and it was before > that time (found) in the Holy Qur'an (and recited by the Muslims). [34 > Muslim, II, No. 3421.]