When management say they want to minimise support costs by settling on a single enterprise platform for websites what this can mean is that they are stifling an organisation's flexibility and capacity to innovate. Big enterprise systems often lack functionality that, while not traditionally popular in a corporate environment, can be highly popular across the general internet (social media being a case in point) or for specialist tasks. By their very nature, it can be relatively difficult to add functionality to such systems, especially when you do not want to impact upon their stability and usability of the main websites. The response, which may be valid, is usually that by using a single system you can take advantage of integration across your platform.
Allowing non-integrated third party platforms to be installed may increase support risks, but it can have allow organisations to rapidly respond to users' and customers' needs and enhancing satisfaction. As such, it should be considered as a valid strategy.