This is easily explained. Many ACGME programs will accept your COMLEX score for the purpose of residency application.
Also I question this notion that a majority of osteopathic students do not take the USMLE. If you add together the number of students who take
either USMLE Step 1 or Step 2 or Step 3, you'd have a majority. Some residency program director like to see that you've taken either Step 1 or 2, just to verify that you are on par with their other applicants, but they don't necessarily care that you've taken both.
Here's another source that discusses this issue, and demonstrates this was as true 10 years ago, as it is today.
Source: Wilson, JF.
Osteopathic medicine's growing pains. November 1997 American College of Physicians Observer
Unless your statements are sourced, they don't hold much sway with me.
bth