There's a reason for this. In large systems the need for a fast switch from utility to inverter power under full load requires that there be a battery charger constantly charging a battery bank and an inverter or rack of inverters connected to the battery bank to provide power to the load. This isn't very efficient but it works well.
I think this is partly what he was talking about. IE, instead of having a UPS which converts battery power to AC while simultaneously charging the batteries, just have a big DC power supply, float the batteries on it, and use that to power all of the servers and stuff. This does make sense; I have a similar setup with a Mini-ITX motherboard I use as a home mail server and some other things - it has the 12 volt car power supply in it, along with a small 12 volt gel cell battery for backup.
Also battery voltage can vary from about 10 V to 14.4V per battery so I don't think this is tightly regulated enough for computer components. In a large system you want to keep the DC voltage high so your I^2*R power loss is minimalized so DC voltages as high as 108 V are not unheard of.
I think there are commercial systems that operate with DC like this; I know for the telecom 48 VDC is used a lot. This is still a manageable voltage, as high voltage DC is a little more difficult to work with than AC at similar RMS voltages (though I'm sure higher voltages like 108 VDC are used too), but you don't need absolutely huge wire. Also, there are low voltage DC-input ATX power supplies available. I've seen them for 12, 24, and 48 volts. Generally they will produce a regulated output for the PC, so if the battery voltage fluctuates somewhat it's not much of a problem, provided it's within spec. Also, normal AC units usually work by rectifying the incoming line to DC, and then using a step-down converter to get the lower DC voltages. So you could probably run one directly off of 170 VDC (170 volts is around the peak of the AC sine wave).
And of course, if you have a system like this it wouldn't be that hard to throw some photovoltaics in too, which would reduce the load on the main power supply (and thus the draw from the grid).