upon the start of a login shell, the bash will consult the below files in this order:
1. /etc/profile
2. ~.bash_profile
3. ~.bash_login
4. ~.profile
when you start a nonlogin shell, bash consults only ~bashrc.

so there is a difference between them. however, thats not to say osx is different. i'm not sure about this. this is more typical of linux/solaris.