Dear Archna,
I think Paulomi, Bhushan, micoKrish, rkandadai and ragamuffin99 have all put in very salient (good) points.
However, I would like to add my own views :
Firstly, money becomes the main motivator when an individual is genuinely not making enough money to meet his most pressing needs; in such a case, he will keep on changing jobs until he comes to a level where he can relax a little and consider motivational factors other than money; in most cases, he will then settle down and make a change only if another job offers him more motivation (even if it does not offer him more money). This is, of course, assuming that his work output continues to keep pace with the money he earns, and he is worth being retained by the employer. He can also be frank with his employer and tell him why he has to look for another position, and if his employer feels he is good enough, then his money can be enhanced, enough to retain him.
There are youngsters, however, who look only for money - more money - and jump from job to job only because more money is offered in each case; such a person does not care for motivation other than money, and has no staying power. If you try to retain such a youngster by offering him more and more money, you will end up by giving him more money than he is worth - and he becomes unproductive dead wood. Such a person can be easily identified from his past work history, and should not be taken on in the first place; you may realise his motives only after you have employed him; in such a case, do not try to retain him when he mentions he has received a better offer. Let him go.
Paulomi and the others are also right when they say that each individual case is to be viewed in its own light. No generalisations can be made.
Also, from a personal viewpoint, though Maslow et al's theories are very thought provoking, they are only guides, and not to be treated as gospel truth.
I think you have enough matter to be able to convince your Manager that he should keep an open mind, and treat each individual case on its own merits!
Jeroo