My dear Manish, your initial question seems to be very logical and reasonable. As such, it's a right question. All questions are right, but the answers may go wrong because it is imperative that the questions alone should not be answered, but the questioner too.
After reading the answer of "Consult me," I am very sorry you've posed a wrong follow-up question. The answer was not that prescribing a period of probation, even for an experienced hand, is a must in every perspective. The period of probation he suggested is not with reference to the incumbent's assignment but solely to that of the people and the work culture of the organization - that's all. Then, why do you become so legalistic? Law cannot solve all problems. Problems are self-perpetuating, and therefore all laws are in a flux. What the law sets down are minimum standards with reference to the mischiefs it aims at rectifying. No law prescribes that there should be a period of probation or an age of superannuation!