TKIP vs Broadcast Key Rotation

In some of the Cisco documentation, they state that broadcast key rotation
(BKR) "is an excellent alternative to TKIP if your wireless LAN supports
wireless client devices that are not Cisco devices or that cannot be
upgraded to the latest firmware for Cisco client devices."

I don't really understand how this is true. If BKR is only rotating the keys
for broadcast frames, then the user's session (unicast) key isn't touched
by this mechanism, right? So, the classic WEP cracking vulnerabilities
still apply, right?

Must be something I'm missing here... who can enlighten me?

Thanks,
Mike