Basically: "you're about to have a high income and—as a class—have a very low default rate. We'll let you put 0% down and not count your student debt against you". Usually before you get your first paycheck (just need to show them the contract).
FWIW I'd argue that tech workers are—financially speaking—much more varied than doctors, who generally exit residency, get a position (sometimes in a new city) and see their income skyrocket. So I can't say this is perhaps as justifiable an idea as it is for new doctors, but I can buy the rationale for certain workers.
If you're in the boat of "I could afford a mortgage around here, but would take years to save a huge downpayment on these prices", the doctor mortgage can be a great thing. Not least of all because it's not always savvy to make a big downpayment: http://themortgagereports.com/18520/20-percent-downpayment-r...