Where do you get that idea?
In our FM practice, we take care of people who are on ventilators, who are paraplegics, who have severe CP, etc. In my patient panel, I have someone with advanced MS who needs a lot of help and a lot of care. They're just as sick, if not sicker, than the people I took care of on IM as a med student.
And looking at average salary doesn't make any sense - people who specialize but still keep up their IM board certification get included in those averages, which artificially raises them. A general outpatient IM physician doesn't often make much more than a general outpatient FM physician, if they have similar patient populations. The only difference is if the FM physician sees a lot of children (who often do not have great health insurance) or if they do a lot of OB (and have to pay much higher malpractice premiums).
Don't forget - if you do an FM residency, not only will you have to do peds, you will have to do a lot more obstetrics/gynecology/women's health than you would in an IM residency. A LOT more.
Meh. I think that that's up for debate. My inbox gets filled every week with recruiters offering hospitalist positions for FP in urban areas.