The ADB driver usually only shows up when the device is in USB debugging mode. Unless you have a need for this mode to be on (if you have aren't sure, you don't) you should turn it off. You can do so by going to Settings > Applications > Development.
The stores have to turn on USB Debugging and Stay Awake to temporarily side-load the software to transfer contacts to the Android phones. Occasionally the rep may forget to disable these after doing the transfer. USB Debugging mode can also cause issues when trying to use the standard USB Disk Drive mode to your PC.
As long as you are connected to the internet Windows will automatically download the correct drivers for the phone. If you aren't using Windows my knowledge is much more limited. Most Android phones behave in similar fashion when plugged into USB so there shouldn't be a huge different between the EVO and my Hero.
I don't notice anything out of the ordinary in Device Manager saying HTC when I plug my phone in for charging only. I only notice a new Disk Drive when setting it into USB Disk Drive mode (as expected). Most of the drivers that are installed when the phone is plugged in have to deal with the basic USB features such as power transfer and device recognition which are built-in, they just are assigned automatically by Windows. The only other driver you may need would be included in the HTC Sync software which is preloaded on the microSD card for you to install on your PC. That is only needed if you want to sync the device with your computer.