No exclusions, but did you set up a shipping cost for the USA?
If you didn't, then your item will not show up on dotCOM.
Use Revise to correct this.
There is a known problem where the Canadian service is slightly smaller than the equivalent USPS service and shows that message even though you think you have ensabled US shipping.
Again go to Revise and fiddle with the dimensions until the US S&H shows.
I never can remember what those dimensions are, but pjcdn is the expert and may be along to help.