As someone who has a long history with BMX bikes before recently making the leap to fixed gear (my back couldn't take it!)...I raced semi-pro some years back and continue to be somewhat of an old-school BMX enthusiast...I can assure you that the the statement of track rings being "more round" couldn't be more false. It's a sh*tty component maker that creates bad chainrings...BMX, track or otherwise.
The biggest difference is that BMX chainrings usually have 110 bolt spacing, meaning more chainring/less crank arm spider than "track" cranks/rings when you move into 40+ teeth territory.
Hope that helps (at least a little).
Last edited by Scrodzilla; 06-18-09 at 07:16 PM.