I think it's a chicken and egg thing -- are they not teaching for the boards and thus not scoring that well, or are they not scoring that well and then claiming that they are not teaching for the boards.
In fact Step 1 has less to do with targeted teaching and more to do with individual preparation. Most med school courses cover all the basics, some spend more time on some details than others. But all med students study from the same First Aid, Q-bank etc. If you have gotten through those two (or other comparable) resources, you have studied for the boards comparably to 90% of the folks who take it. If you look at some of the truest focused just "teach for the boards" type schools -- some of those in the caribbean, you will see that the board pass rates tend not to be particularly good, reinforcing the notion that it is a matter of individual effort and ability, not anything the school can manage for you.