From the registration information section at
http://www.baa.org
"The B.A.A. reserves the right to reject any entry, issue special invitations, cancel the race, expand or further limit the field, or adjust the entry procedures.
The Boston Marathon includes a field of elite, invited athletes. Regardless of qualifying performance, selection and entry into the elite field is subject to review, and acceptances will be made on a limited basis. Entry into the field of elite, invited athletes will be at the sole discretion of the B.A.A.
Entry into the Boston Marathon will be at the discretion of the B.A.A."
To the OP, you're upset that the BAA has chosen to invite foreign athletes who wish to travel to the US and run. More importantly, you're upset because these foreign athletes are taking up spaces that could go to American runners who missed the registration cutoff. So what? That's the BAA's choice. They state it very clearly on their website.
It sounds to me like you're whining. If you have a problem with the BAA and how they do things, then don't run the race. There has to be over 100 marathons in the US each year ... just pick another one.