No vendor specific protocol should be used on your network. No vendor specific software should be used in the concept. No vendor specific hardware should be needed. Proprietary technology limits the scope of vendors, but on the other hand - cost and technology do not benefit from monopoly.
A splendid example of the consequences of vendor specific technology is Active-X. Many thin client solutions utilize web-technology with incorporated Active-X objects. Active-X is a Microsoft specific technology, and by using it these solutions limits the scope of client operating systems to one vendor only. For example cumputers running Unix, Solaris, MacOS, OS/2, BeOS, etc. cannot use Active-X.
Open standards simplify maintenance and troubleshooting, since a wide range of tools are available. Likewise, knowledge about open standard components is more spread than about vendor specific solutions.
Vendor specific solutions often have a price. The costs for such solutions are often far higher than for open standard solutions. The cost is not only depending on license policies. Other factors, such as a limited market for components and support, influence the cost as well. Unfortunately, these factors are often overseen.