Those pass rates (89 and 94) are overall for DO and MD in 2013.
DMU's pass rate is 91.2% for 2013 per the handout (it was higher several years prior).
Also, what I'm saying is that the US DO average step 1 is about 215 for the self selected test takers, as is evident from the averages taken at 3 of the better schools (over 10% of the DOs who took the exam and a pretty good sample size). Not that this drags the overall average down much based on the quantity taking the exam vs US and foreign MD. I think it is conservative to assume the US MD average is only 227 (it is probably a point or two higher) since many school's average are above this and at least one group of the examinees is below. And the difference of 1/2 a standard deviation or more is significant and something to consider when deciding on schools.
As for a citation on who takes the USMLE at osteopathic schools this seems a bit unnecessary. It is an optional extra board exam taken to land more desirable (on average) ACGME residencies. From the schools I've visited and those I've spoken to (several dozen students) the bottom of the barrel of the class skips out on taking it and generally only the average to above average pursue the more competitive residency options in the ACGME that require a USMLE score (some less competitive programs do not require the score) thus they are not in the discussion. At DMU only 45-70 people per year take it, to give a rough idea and this is per data given at the interview.
There is no data I know of about US born foreign MD, but I would guess they are the lowest average based on their match rates, with foreign born foreign MDs being higher due to some influx of prestigious international grads (Oxford etc.) bringing there averages up.
When I was looking to apply there was no data on this at all. That is why at every school I interviewed at I made sure to inquire and find out for myself. Now I'm trying to pass it on so people can be informed as possible.
Does a higher board score mean you'll be a better doctor?... No
Does a higher board score mean you'll have an easier chance at the residency you want?...
Yes, and that's the #1 reason it matters, because we all would like to match in our own fields and locations of interest