A large part of fellowships is about who you know...or more accurately, who your attendings know.
The background and connections of your current attendings are the keys to getting fellowships. Certain attendings are well connected at certain programs. After having worked with you for several years, they are more than able to vouch for your ablilities, knowledge, work ethic, personality, and character. All it takes is a phone call from them giving the word to someone they know and you are in.
Many attendings in academia have good connections with each other because of the nature of what they do. The academic types tend to "get off" more on their connections, it makes them feel more important in the academic world to know someone with a big name or from a big name place.
That being said, I wouldn't dismiss community programs. From an attending perspective, community program positions are EXTREMELY desirable, especially to those who are academically oriented. You are involved in resident education, you can pursue research under no pressure, you never take overnight call because residents take it for you for free, and you make big private practice type money. Because of this, community program practices are able to select extremely high caliber trained people to work for them. I know of a community program with attendings with fellowships from UCSF, MGH, Duke, UCSD, etc. It's no coincidence that this community program routinely matches residents at these institutions for fellowships.
My point in saying all of this is don't overthink yourself. 98% of radiology programs are going to give you solid training to be a very good radiologist as long as you put in the effort. It's your job to pick the right place for you when you interview. Don't pick a place based on what you think other people might think. Pick the place where you are most comfortable and where you think that you will be happy and fit in the best. Take into account factors that are important to YOU...ie location, call schedule, personality of other residents, etc. Don't worry so much about what other people think of the place. I promise as long as you put forth a decent effort during residency things will work out OK no matter where you go. If that's the case, you might as well go somewhere that YOU will like!
