I'm a strong believer that a computer should be more aware of its environment.12v Molex fans don't serve that purpose well.
I don't see a huge need in the PC to know how fast it's larger case fans are going. So long as it knows it's vital CPU and chipset fans are operational.
It's not how fast a particular fan is going per se (though that has its particular uses), it's more important for the PC to be aware the fans are actually functioning. I have a BH6 with melted standoffs because the 12v case fan seized and I had absolutely no idea that happened. I also have a TNT card with melted chips (though the iron horse is still perfectly functional) because the 12v internal fan circulating air failed. I could go on and on with the horror stories when a fan failed and none of the fail safes kicked in.
One another note. Why not? The functionality is there, one should take full advantage of what it offers (though I also believe in having full flexibility in
not having said fan if the need should arise).
That said, my desktop, it doesn't even have EDID communication with the 24" monitor. I had to manually tell it what resolutions the monitor supported. 
I can top that, I have a PC that is completely headless.

Which reminds me, I have to find the rest of the case.