This is my understanding. Root means allowing access to the OS as if you are a software developer. In this way, you can install custom Roms other than the one provided by the manufacturer.
The problem is that manufacturers don't like you doing that. So, they restrict your access by creating a "firewall," the SPL (Second Program Loader). This is the actual software that permits the Rom to initiate. SPL is usually "perfected" when new. That is, it is impossible to crack it up to allow a user the privilege to install new Roms.
It has been my understanding, after reading tons of info from XDA and the related Wikis for HTC Androids, that developers sometimes find software vulnerability when a newer version of the SPL becomes available and thus are able to root the phone.
If you are interested in rooting this phone, please go to the XDA forum for X10 development. There is a thread in which various developers are trying to find a way to gain root access for this phone.
Although XDA is mainly a HTC forum, their knowledge about rooting is endlessly better than other forums because they have been at it longer than other. They started with the windows mobile systems.