I absolutely think that statement is too good to be true.
I just read through MTB3 2 weeks ago, and while it covers alot of stuff, I still think it lacks a lot of info. Especially the Surgery and Psychiatry sections seemed thin.
This week I'm reading through MTB2, which I used for step 2 and annotated while reading through the Kaplan notes. That has all the info I need (but only because I annotated it 6 months ago).
However, I do think that an US graduate in an US residency position should be able to do fine with MTB3 and Uworld as their only resources (just too bad that I'm an IMG who haven't entered residency yet - only went through intern year in my home country).
Good luck with your studying and exam...