That's a great point. However, don't forget that a "more than 2% shareholder" or an S-Corp can deduct 100% of their health insurance premiums just like a sole proprietor.
That being said, my understanding is that an owner of an S-Corp can't participate in their company's HRA (health reimbursement accounts). So if a person has a lot of unreimbursed medical expenses, the C-corp would let them set up an HRA and make those costs deductible.
The pitfalls of a C-corp usually outweigh that advantage. A C-corp is subject to the risk of double taxation on any profits kept in the corp one year and then paid out to the owner the following year. Plus, the corporate tax rate on Personal Service Corps, which includes physician corporations, is the highest individual tax rate plus 1%. Finally, the year you sell your practice, you might not get the full benefit of the lower capital gains rate since the assets of your practice are held by the C-Corp.
Let's say you want to purchase a car for your practice. You take $30k of profits and purchase the car. The problem is that the first year depreciation for an automobile is limited to just $11k in 2008. So, if you start the year with no money in your practice's bank account, and end the year with no money in your bank account, the corporation will show $19k of profit thanks to the auto purchase. The PSC tax on $19k at 35% is $7k!!! That's a big pitfall of not electing S-Status.