well i've got 2x120JBs along with 2x80BBs and 1 seagate cuda IV, I HIGHLY RECOMMEND FANS NO MATTER WHAT, here is my reasoning. I have a "twitchy" power connector on my Enermax PSU and I used to run most of my fans (I have 4x80mm Intake enermax thermal sensed fans, 2x the same thing exhaust and a 120mm side intake over the CPU/ram) off that one connector. I never realized how important those fans were until that "twitchy" connector decided to "twitch" and most of the fans minus only the CPU and the 2 PSU fans went dead for about 6 hours while I was away. When I opened my case after immdiatley shutting down I thought I had lost everything because a blast of heat came out of my machine and the interior metal was almost burning to the touch, seems it acted like a hugh heatsink for all my hard drives after the fans died. Which in retrospect is a good thing because the more heat that interior metal takes away and the more you blow over it and the drives the better off you are. So while no it's not necessary, you will find your drives will heat up quite a bit.
Hope this helps to reiterate the need for adequate cooling for not just the mobo components but ur drives as well.