Obligatory Wikipedia link: http://en.wikipedia.org/wiki/ZigBee
802.15.4 defines the standard that these guys are using - also known as ZigBee. ZigBee is a lower powered WPAN type of "mesh" networking used in things like smart building communications.
There are generally two options for frequency - "900MHz" and "2.4GHz". They operate in a mesh network typically (or virtual star), but usually do so at lower powers. What isn't being fully called out is that most 2.4GHz devices will cause nasty interference to Zigbee, since they typically run at lower powers (0dBm or 1mW) at channel widths of 5MHz (802.11b/g/n uses 20MHz channels by default), using similar encoding as the older 802.11b protocol. Most consumer WiFi routers run between 40mW to 100mW (~16dBm to 20dBm). 1mW (0dBm) will most likely look like noise to WiFi. If the meter operator was considerate, they'd pick one of the few channels that lies between or just outside the typical WiFi 1, 6, or 11 spaces (eff those guys who use channel "3" or "10"). That all said, if the meters are using a ZigBee Pro implementation, they may be transmitting at a much higher level - up to 100mW (20dBm), which would be quite intrusive to WiFi if using a ZigBee channel that overlaps WiFi. Anyone affected by that would HAVE to use a different channel if the meter or meters were constantly transmitting.
In my profession, I'm part of a team that supports the deployment and operation of some very large warehouse WiFi deployments (both 2.4GHz and 5GHz), and thus we're quite protective of the 2.4GHz band within the four walls. I can't tell you how often we've been approached by people who want to deploy ZigBee building controls in this band, each time refusing them since we know we'll make each other's lives miserable. Our 802.11 operation will likely render their equipment useless. We let them know that 900MHz or wired RS422 are both fantastic options in this case.
I bet the power company didn't consider the alternatives... or just didn't know and/or care. Not everyone is an RF expert, and the "wireless" buzz-word wins in may board rooms especially if it saves money.