I think that many doctors, even those who may be motivated by money, wouldn't go that far. Yeah there might be people who would, but I think more or less what most people will do is go into a field where they could do their job well but go into a field they know will be lucrative and well rewarded if money is their goal. Or in some cases, if they have a creative mind and entrepenurial spirit, they'll start something on the side and invest their money in a way that the profits will return many times over.
As an example, I always use the example of Dr. Kiran C. Patel in Tampa and his wife.
Dr. K.C. Patel is worth over a net worth of 600 million dollars. Yeah you heard that right. What did he do?? He started an HMO company in partner with his wife who is also a doctor and their doctor relatives. Wellcare health plans. Then he sold it..
He also invests in lots of philanthropic endeavors which has won him many local and national awards.
There are other ways of bringing your MD to use even if that is your goal. It isn't mine but I don't doubt there are those out there who kind of are doing this for financial reasons. Partly, its the desire to be educated and partly the desire to be well off that drives many of the people I know into medicine.
In Indian society, being educated is to be respected, but to be educated and making a high earning potential is a big deal. It is not what influenced me into medicine, there are more personal reasons for that, however I've seen it to be true with many family friends I know.