SiteVision, EpiServer, Sitecore, Escenic and Polopoly are some of the examples of the first generation content management systems (CMS). They are typically characterized by the fact that customized or new functionalities are added through the development of new modules that are also programmed in .NET or the Java platform. This is actually time consuming and also requires help from experts. In reality, what it boils down to is that a monopoly-like scenario is created where you become completely dependent on the limited number of service providers for making even small changes or development.
Drupal content management system, on the other hand, is a second generation content management system. It signifies that a new or customized features or functionalities can be developed in the user interface without programming. This task does not consume much time, and it can be performed by any member of your staff who is well-versed in your operations. That way, you will not have to depend too much on professional service providers (Drupal developers). Hence you can make minor changes or adjustments yourself wherever the need arises.
However, even Drupal content management system requires programming at some point of time, for tasks like integrating other systems into your own operations. You need not worry and lose sleep over this issue because, unlike EpiServer and SiteVision, Drupal is also free software with open source. This simply means that Drupal is available for free, and you can use or modify it to your heart’s content. It is you who will have the liberty to distribute or change the modifications. But whenever you make any changes, make sure you do it under the same terms you obtained Drupal CMS i.e. an open source license.