Hey mbhound,
This is actually something we had implemented about a year and a half ago, unfortunately didn't work out for a few reasons.
The first reason was that the actual plugin for the generic call admin system is extremely finicky. Sometimes it would just not work, and other times it would crash the server entirely. It took me forever to chase down the cause of this, and with no fix (or reason why it caused crashes), the possibility of an entire server crash due to a call admin command just isn't feasible.
The second reason against this was due to the sheer number of people abusing the system. No matter how hard we warned and enforced against abusing the system, it still happened quite often.
Part of the reason for donors getting votemute/gag access is pretty much a trust thing. Prior to donors getting access to this, votemute/gag was available for the general public and that was also abused as hell. Donors generally get a bit more trust - you guys have monetarily supported the servers and community, meaning you have invested yourself into the betterment of the community (which is always appreciated!). That being said, I believe there is a much, much lower chance of votemute/gag getting abused, than being available to the general public.
Anyways, I'm straying a bit too far off topic. I have added several new admins around this holiday season, and we've definitely been getting more coverage (thank you guys!), but obviously admins aren't on 24/7. Don't get me wrong - I do agree with you and I believe some sort of call admin system would be extremely beneficial, and I'll start looking into alternatives for the meantime.