Ah yes the dreaded registry.
On my Linux machines, if I want to rebuild a server all I need to do is a clean install followed by apt-get/yum install and then in the vast majority of cases you simply copy a configuration file over from the old machine. Voila! The job is done in an hour.
Back in the day you could do much the same with Windows. In fact I remember the time when you could simply copy the MS Office directory from machine A to machine B and it would work perfectly fine.
This is clearly a less than ideal situation from the perspective of the company who is trying to sell you MS Office however and thusly the Windows registry was born.
With the registry in place the configuration part of any particular application is disconnected from the application itself and placed into a binary blob that is impossible to copy. To obscure things even more the configuration for an application such as, for example, MS Office, is peppered throughout the registry instead of residing in its own "branch" of the tree and is therefore mixed in with all the configuration details of all the other applications in the system. Further obfuscation is achieved by "hiding" binary stuff (ie "non ascii") and borking the registry editing tool so that it will not allow you to even see the "non ascii" parts let alone edit them and we have a sufficiently tangled mess that the only possible way to install something now is to go through the complete install process which requires access to install media and the associated DRM hoops that must be jumped through.
I invite people to do a search in their registry for the keyword "outlook" and behold the thousands of references littered throughout the directory tree. Then imagine that multiplied by the number of applications that you have installed. It is little wonder that the registry is constantly bloating up and that uninstallers consistently fail to actually uninstall themselves properly.
There is absolutely no valid reason that a product like MS Office requires such a ludicrously complicated and widely dispersed configuration other than as a means for Microsoft to create such a complex mess of details so as to make using illicit copies of their software more difficult.
For the numbskulls earlier in this thread who have bought into the whole "but its a database and couldn't be done in any other way" nonsense you really should not be commenting on stuff you know nothing about.