Returning it because of the fan is certainly on the more extreme end of reactions, but it simply depends on the use case and the user. For example, I use an Axe III as the audio interface of my PC, which means it's turned on for as long as my PC is on, which is basically whenever I'm home and not sleeping. Of course the PC is in the main room of my flat where I spend almost all of my time. The fan on the Axe is about as loud as my PC fans during normal operation (not gaming, not a heat wave outside), meaning the Axe FX roughly doubles the ambient noise level. I personally can live with that and it's not yet annoyed me enough to put in another fan, but it certainly took a week or two to get used to it. In fact, one of the first things I did after I turned the Axe FX on was searching on this forum if the noise level of my unit was normal.This is actually sort of funny. "I can hear the fan" as the main reason to send it back.
If somebody with a similar use case has a lower noise tolerance I can certainly understand them wanting the Axe FX to be as silent as possible. There's people who build noiseless (home) recording studios with silent PCs etc where the Axe FX might end up being both the most expensive and noisiest component of the whole setup. Of course it's not an issue while playing, even in a home recording context (except maybe for ambient stuff or for people who set their monitoring level really low). But I bet you a lot more people than just me are sitting in front of a turned-on Axe FX for hours without touching a guitar.
I can't find Cliff's alleged quote on TGP, but assuming that it is correct and they upgraded the Axe III to a temperature controlled fan, I think Fractal know that ambient noise is a serious factor for some people. On the other hand, they're a small company and have only so many resources and a lot of other things that are probably higher on their list of priorities. Personally, I will gladly take another modeling epiphany or additional amp/fx types or a free IR pack etc over a less noisy unit. But I would still love it if the Axe FX IV, which I will certainly buy some time in the 2020s, was noiseless