As far as I can tell there is nothing in google's terms of service that relate to defaults. How do I know this? Because Samsung replaces every app I can think of with theirs.

- launcher - web browser - mail - calendar - keyboard - SMS/MMS texting app

Not to mention the entire "skin" of the operating system including added and removed functionality.

Samsung even has their own app store on the phone.

All of the above apps are very much the default for their type (when such a concept exists) and in some cases, like email and calendaring, you can't set another program as the default (at least not through normal consumer friendly means).

What "default" are you actually referring to?