This is really really bad advise. See Dr. Mcninja's reply below, he's not exaggerating--if anything, I think his estimate that your $12-15k Roth IRA investment during residency being worth $300k when you retire is probably low.
I think people are confused about retirement savings. Most of these save early articles are written to sell lots of magazines/web advertising revenue, and so are targeted at average shmoes who will have only a slight increase in annual earnings per year. If you're making $50K per year at age 27 as a low-level engineer or business person, and expect to have a slow annual increase in wages up to maybe $80K when you retire, it makes sense to save early and start compounding, because there is no pot of gold under the rainbow awaiting you.
However, if you're a doctor, it's kind of poor advice-- because your earnings and investment opportunities once you're in practice are just so superior to your earnings potential during residency. Specifically, once you are in private practice, you can fund your own SIMPLE, KEOGH, or other pension plan to the tune of $45,000 per year (as compared to the pathetic $4K per year of the IRA). That will be a pre-tax contribution, which is actually of significant value (comparable to the pay tax now, pay no tax at retirement roth structure) to you as a physician since the marginal dollars going into your retirement plan based off your $140K per year starting salary (you can double this if you're in a surgical specialty, gas, rads, derm, etc.) will be taxed at around 40+% depending on your state of residence. One year of living tightly as an attending, and you'll be able to save way more than you could during four or five years of similar living as a resident.
In short, if you want to be "set for life"-- don't screw yourself during residency when you're already screwed, but instead live tightly during your first couple of years in practice, when you could sock away several hundred grand in a tax-deferred account that actually will make you a millionaire when you retire even if you don't save anything later in life.
Or, alternately, just live reasonably when you're an attending, stick $20K, $30K per year in a retirement plan from when you start, and you'll be very happy by the time your retire.