you make a good question K.Venugopal
to a non-muslim using the Qur'an doesn't count as evidence so i will answer you without making reference to it's verses.
at the time when the abrogations occurred, the Qur'an, which muslims consider a Guidance and a Law, had not yet been completed. if you know about the history of the Qur'an and how it was revealed, you will find that it's verses and chapters are divided into many categories.
the verses were revealed in three main categories:
1. Those of the Past
2. Those of the Future
3. Those of the Present
Those of the present are those which were revealed about the time of the Prophet peace be upon him and they are divided into 2 main categories. two such verses are chapter 111 and 112.
Chapter 111 was revealed as a response to the Uncle of the Prophet, Abu Lahab after having criticized Muhammed peace be upon him for gathering his family members and called them to islam.
Chapter 112 was revealed as a response to the Pagan Makkans who asked the Prophet peace be upon him for the lineage of Allah.
all the verses of the Qur'an have their own history, the commentators have gathered all the relevant information that have to do with every verse and chapter.
Based on that information which i have given you, the following should make sense insha Allah (God willing).
whenever a special case occurred, Allah would reveal a verse for that specific case. but since the Qur'an had not been completed, Allah would then abrogate that. the abrogation of verses is divided into 3 categories also, one of those categories is that the text of an abrogated verse remained however it has/had to do with a specific person, like chapter 111 (this does apply to others in a way), or the verses that clear the wife of the Prophet peace be upon him from having committed adultery when the people accused her of such an act. it has nothing to do with the other muslims, however it is a verse that speaks of the case, it was something that only Allah could clear her from the false accusations so Allah revealed the verses and they remain in the Qur'an to this day and till the end of this world.
so on that, now that the Qur'an is complete, nothing more needs abrogating, since muslims believe that the Qur'an needs not to change from when it was revealed up to the Day of Judgement. we accept it as the Perfect Law of Allah, a book, a guide and law which was completed over 1400 years ago. something that is not complete may need changes, but once something is complete it doesn't need change. and the abrogations cannot be viewed as Allah making a mistake, some were verses of specific cases that have nothing to do with everyone else, like the verses relating to the wife of the Prophet peace be upon him. i cannot speak about all the abrogated verses since i do not know about all of them.
i hope my answer is helpful, a bit long but i couldn't explain it if i had made my reply any shorter.
please let me know if that doesn't answer your question.