This isn't raising money for just direct medical expenses; if you work as a contractor, consultant, speaker, etc., and for some reason can't work for a few months, it doesn't really matter if all your medical expenses are paid 100% -- you have no income, and for a lot of people, that means paying regular bills becomes difficult. It's not like your rent expenses at home go away just because you're staying in a hospital instead.
Getting disability insurance is strongly encouraged for contractors and others in the US (we have both short term and long term).
There are actually federal (and some state) programs to pay disability if a worker is disabled, but enrollment takes some time, and generally the support is at poverty level, not based on salary.
A serious complication for people who freelance, contract, etc. is that aside from Social Security Disability (SSI, generally for long-term disability), the programs are related to unemployment insurance, which is related to wage income. If you, for instance, are bootstrapping a company from savings and not paying yourself a salary, then get in an accident, even if your medical insurance covers 100% of medical costs, you're probably screwed on everything else.
