That is how it generally works, but if you go to your mail server and forward your mail to the BB addy, then the pop3 mail is instant, too.
I know, because, I initially set up my account on the BIS and let it do the polling, I didn't know any better. Then I noticed on the FAQ here how to forward your mail instead of setting it up on the BIS. I initially set it up both ways and got 2 copies of my pop3 mail, about 15 minutes apart. Once I got it working, I went back into the BIS and deleted all my pop3 addys which also erased my "sent-from" addy. I had to go back in & add the "sent-from" back and have been a happy Instant receiver since