That information is completely outdated.
The job market for radiology is tremendous right now. There is a huge demand, and not enough radiologists to go around. You should see some of the packages (salary/vacation/perks) that people are being offered. It is truly mind-boggling. Clinicians are ordering imaging studies at an increasing (alarming?) rate, which is generating a lot of business. This isn't likely to slow down anytime soon, and as long as the standard of care mandates that films be read by a radiologist, the field will be lucrative.
Fellowships are common, especially for residents trained in a university setting, but they are not required for general (i.e. non-interventional) radiologists. Most fellowships only last one year, so aside from putting off a potential influx of cash, the marginal cost of another year of training is pretty low.
The future of radiology is bright. Iserson is full of crap.