Response: I thank you for your reply. However, what I am trying to seek here is from the point of view of parents themselves. You have said that children should and must show kindness towards their parents and after marital contract, the moral obligations are on respective spouses as well. This point is also well appreciated. But what rights could parents assert upon their son/daughter-in-law? Is serving parents-in-law equally obligatory on children-in-law just as it is on their own children? Or is the wife/husband accountable to their spouse’s rights only? I would appreciate if your response could clearly delineate culture and religion. I am asking purely from the religious point of view. May be, one of the ways to throw light on this could be to look at the cultural practices of marriage and family structures at the time of the Prophet (sws). Perhaps, we may be able to understand in this way, why is there no clear and direct religious teachings on the issue.
    Comment: You have hinted towards a good clue that explains the reason why we don’t find clear instructions of the Prophet (sws) in this matter. Actually, there was no need to since every person would settle in a separate home, and there was no concept of joint family system nor did they abhor the thought of their mother marrying someone else after the demise of their father. So much so, they would keep even their wives in separate homes. As you may know, the Prophet (sws) himself provided separate homes to his wives near the Mosque of the Prophet in Madinah. Thus, there was virtually no question about the rights of the in laws. 
However, as far as my previous reply is considered, there is a very interesting point to note as compared with the question you have again put forth. You write:

What I am trying to seek here is from the point of view of parents themselves?  

    And:

But what rights could parents assert upon their son/daughter-in-law? 

    In my reply I had concluded: ‘As an obvious corollary of this agreement, her relations become yours and yours hers. It is for this reason that I opine that the aforementioned directive of treating your parents well extend to your spouse’s parents as well. You are indeed obligated to show kindness to them as you do to your own’. 
    Although this statement is from the perspective of children, I think that it equally means that your spouse’s parents are in the capacity to seek whatever help they need from you, after you have assumed the position of their son-in-law, just as your own parents can. 
    I, though, agree that this expectation of help and service is likely to be more on your wife from your parent’s side than on you by her parents. It is the way this world has been designed. Parents feel more comfortable living with their sons instead of their daughters. Consequently, the demand for service is more likely to fall on the wives’ side. However, it does not mean that in any case, if your wife’s parents seek your shelter and help, the obligation that rests with you is less intensive than that with your wife in respect of your parents. 
    You have asked whether it is obligatory to be of service to your spouse’s parents as it is with your own parents. With all due respect, I would like to say that it is not good to view every thing in this perspective. We must not divide everything between the obligatory and the allowable and between the allowed and the forbidden. We are, indeed, moral beings. The sense of morality that we are innately blessed with guides us to the way we should live our life in this world. We must comply with the dictates of this sense no matter if it is obligatory or recommended. Thus, keeping in view the essence of Islamic teachings, and the instructions of intuition, I daresay a person will be held accountable on the Last Day if he did not help a ‘stranger’ when he could, not to mention his in laws. No doubt, the extent of our duty changes as the nature of relationship changes, and surely our intuition and conscience would help us decide in this respect. But, I again assert that, as far as your spouse’s parents and your own parents are concerned, I see no difference regarding the provision of service and help.