The site My OB Said WHAT?!? sums up a paradox that many hospital visitors have noticed:
“You’re not ready to leave until you can walk out of here.” – L&D Nurse to mom being wheeled out upon discharge.
Many hospitals do hold to a formal policy on the subject. Thus Methodist Hospital of Houston: “When your doctor has discharged you and you are ready to leave, you will be escorted out in a wheelchair by hospital staff.” Why necessarily in a wheelchair, when you may be perfectly capable of walking?
The Chamber-backed Southeast Texas Record has a theory. It’s the same theory endorsed at Yahoo Answers. As for whether patients actually fall and hurt themselves on the way out of the hospital, it appears from this Eastern District of Pennsylvania case (PDF) that, yes, it happens.