I have heard this as well. The reason is simple, right now with the radiology job market Breast imagers are in greatest shortage, and thus can negotiate the best terms. I know some that are full partner but don't take call and sometimes even do breast exclusively. That would be unheard of for any other specialty. If you do employee track somewhere you can definitely negotiate very high salary for reasonable volume but would probably require onsite or at least hybrid given the breast workflow. Telemammo exists but usually not as full time.
In any case, bottom line is that the lifestyle and comp is better for breast than other specialties, so if you can tolerate the actual work, you should do it. I actually think the advice is true. Problem is, I can't tolerate it and most rads I know can't either, so that's that. I'd rather just take the call.