The exploit that you're referring to is not dependent on firmware but the hardware of the console; meaning it works on all firmwares currently and yet-to-be released. However this exploit requires the need to enter RCM with a jig or equivalent and a device to send payloads with via USB connection. Not everyone wishes to perform this hardmod for CFW as evidenced in this
thread. The unreleased exploit known as Deja Vu and works up to firmwares 4.1 doesn't rely on RCM or a USB cable but rather a network connection; the point is it involves less hardware than the current exploit. Regardless, no one can predict the future or what exploits will be available on what firmware so having a lower firmware is still better than having a higher firmware because it means you have more options available to you. Having unburnt fuses on higher firmwares is the best of both worlds; you reap the benefits of being on a higher firmware while having access to potential exploits on lower firmwares.