You hear a lot of talk about rooting, especially when a new or difficult handset gets rooted. But what many of us forget, especially those new to Android, is that rooting, and having to root phones has nothing to do with openness. A post on the Android Developers Blog reminds us that they are pretty much the opposite of each other. Rooting is, well we've tried to explain it several times and settled with a nice little page about the whole root deal right here. It explains it much better that a few words here will, so it's worth a read.
The Nexus S, and the Nexus One are a bit different. Google specified that these phones have their hardware open to the user. With a few commands, you can set the bootloader to allow the installation of custom software -- "fastboot oem unlock". After that, you can pick and choose what you want running on your phone.
Nick Kralevich, an Android Security engineer, sums it up nicely:
"Legitimately gaining root access to your device is a far cry from most rooting exploits. Traditional rooting attacks are typically performed by exploiting an unpatched security hole on the device. Rooting is not a feature of a device; rather, it is the active exploitation of a known security hole."
The way things are now, carriers have forced users to choose between device openness and perceived security. We can only hope this changes one day. [Android Developer Blog]