Alright, you're comparing apples and oranges. You can't compare starting salaries of private practice ophthalmologists with those of hospitalists and especially not with those of radiologists. The setups are completely different! If you really want to compare, you need to look at the setups and consider the median salaries, not just starting. This is a career you're talking about. Starting salaries don't tell the whole story. After that, you have something to talk about.
Hospitalists are hospital employees, not private practitioners. They are fed patients from the hospital system, and can start with quite a load. They also lose income to those same hospitals. Internists and family practitioners in private practice often start out at under 100k, as they have to build up a practice (see below, as per ophthalmologists). Income potential in private practice is (almost) always superior, but you have to deal with the business aspect of medicine. With the complexities and red tape in that arena nowadays, more docs are opting for less pay and fewer headaches. The median salary for internal medicine physicians in Nov 2009 was about 165k (about 5k less for FP), and this averages over employees and private practitioners.
Radiologists sit in front of a computer, sometimes from home, and look at films all day. If you enjoy that, more power to you. You don't usually have to build a practice. You're hooked up to a hospital and just let the films come to you. You can pour over a pretty high volume of films in a day, and unless you own the scanners (less common than it used to be), the overhead is low. Medicare is catching on to this; thus, the recent slashing in radiology reimbursements with the last CMS realignment (median salary in Nov 2009--prior to realignment--was about 360k).
As an ophthalmologist starting private practice, you usually have to build a patient base, which can take a few years. Even when taking over for a retiring doc, you never start with a complete and functional practice. Most practices will actually lose money on a new associate, at least in the 1st year. You will eventually buy in to that practice. Once you are a partner, the income is usually 2-3 times what you make to start (median salary in Nov 2009 was about 260k; note that ophthalmology actually got an increase with the CMS realignment).
Bottom line is this: don't go into medicine (any specialty) to make money. You'll do okay, but the pay isn't what it used to be and will only be getting worse.
While money may have been a factor in the past, ophthalmology is competitive now because there are only about 23k of us in the US and it offers a good mix of clinic and surgery, has manageable call, as well as better than average earning potential. Likewise, there are about 30k radiologists. There are over 160k primary care docs, just counting internists and family practitioners.
Everyone's entitled to an opinion, though.