In my opinion the only thing .bash_profile should do is source .bashrc, that way the environment is consistent regardless of invocation.
In the example he gives, like many I have seen on the Internet, it tests for .bashrc and if it exists, sources it. But if you didn't test it and for some reason .bashrc didn't exist, what would happen? And if nothing bad would happen, why test for it?
It's just for cleanliness. The script would error out with something along the lines of "No such file or directory".
Thanks. I've never tried it out and was curious if anyone knew.