That is exactly true.
It's a shame that a few people, who have no clue what they're talking about, come here spewing these false claims.
USB is a STANDARD. It means that all devices using it are compatable with this STANDARD. A USB power supply runs at a mean 5 volts, give or take about a 1/4 of a volt. Amperage will vary (high power vs low power) that will affect how fast your device will charge.
I will say that some of the cheapo devices you can buy on Ebay or Amazon are not built to the standards that Verizon or HTC/BlackBerry/etc. power supplies are built to and could potentially cause a problem.
To suggest that a BlackBerry charger would damage an HTC device is as ludicrous as saying that using Energizer AA batteries won't damage your flashlight and Duracell AA batteries will. To suggest otherwise is only showing your ignorance of the subject matter.