I agree. Typically each house has a regulator where the gas line comes up out of the ground. Pressure gets too high, the regulator opens up and vents to atmosphere, much along the same concept of the pressure relief valve on your hot water tank.
However, pressure relieve valves are mechanical devices that can fail and that have limits. The apparently random houses exploded, I think, will eventually be found out not to be random at all. They will probably find the pressure relief valves that failed were all of the same manufacturer/model that couldn't handle the overpressure, or the houses contained an appliance that used the same type/manufacturer of control valve. It might also be found that all the houses connected to the gas mains the same way, which by design or accident allowed more gas at higher pressure to flow into the houses that exploded.
The relief mechanism of the pressure regulator is designed - if you'll pardon the phrase - to only pass so much gas in relief. If the overpressure exceeds the design limits of the regulator, the high pressure passes by the regulator and enters the piping in the house. Appliances, hot water heaters, furnaces, and boilers are also designed within certain parameters. The extra high pressure will ooze, leak, or blow by/around fittings, pilot lights, and control valves.
Leave the high pressure on long enough, and the gas will ooze, leak, or blow by enough to accumulate in the basement. An electronic or standing pilot light would be all that's needed to light off the accumulated gas.
I would not be surprised in the least if the investigation found out the elevated gas pressure was an intentional act. Doing so would cause exactly the type of chaos where apparently random explosions in sufficient quantity to overwhelm emergency responders (and potentially hospitals). Likewise selection of a single utility (as SW noted) where raising the pressure at one point by tampering with the one setting would affect an area large enough to make the news but on a distribution network small enough that it couldn't absorb the high pressure caused.
Consider: any utility will have sensors to detect and alarm when their gas delivery pressure is either too low or too high, and procedures about who is to respond and how. If so, the utility should have responded quickly to the alarms, and before the pressure was too high for too long to blow up houses. I would not be surprised if the utility discovered the alarms were tampered with or disabled as well.