Servers need maintained constantly......there's no way round having to take server(s) offline to carry out such aspects as replacing hardware for instance.
Companies who don't maintain their servers frequently don't usually last too long......especially with the amount of punishment the wgt servers will take......hence they need routine maintenance to keep things right.
I replace my hd's every 18 months max (mines don't get anywhere near the traffic or punishment WGT's servers get), whether they're healthy or not. It's much better to be safe and advise clients of the scheduled maintenance than having to deal with an impromtu hd crash and all hell breaking loose with customers squealing about sudden unannounced downtime.
No one likes downtime but it happens and in a lot of cases it's necessary. That's just one of the pitfalls from operating an online business where the servers receive a great deal of punishment. The only other option is to do less or no maintenance and watch the servers grind to a halt. :)