Why would they? It's not a home server, it's a business product and would usually sit in a server room where noise isn't an issue.
It's aimed firmly at the small business with no in-house IT (well that's what the HP marketing blurb says!). I work with a lot of these types of companies and most of them have their servers (and small servers like the ML110) in a corner of a room, under a desk or, if I'm lucky an old broom cupboard.
In my experience of the ML110 (without additional PCI devices and ambient inlet temp below 23°C), after boot the fans run as follows (as shown in iLO):
F1=31%
F7=13%
F8=10%
And will stay like that as long as you have no PCI devices attached and the temp remains below 23°C.
F8 is the PCI fan I think - if you have no PCI devices inserted, this fan always turns slowly. Add some in PCI devices and F8 will be turning faster after boot.
In addition, once the ambient inlet temperature reaches 23°C, F1 and F7 start to increase in speed as the temp increases and at full pelt they are pretty noisy. If you also have PCI devices attached, then F8 will also react to the temperature increase.
I still see posts about this in the HP forum, but as nothing has been done, I think it's unlikely to be done now. I have considered swapping the stock fans for quieter varieties, but the wiring is a bit unusual and I haven't tried it.