Nice list of vendors. SQL server monitoring tools have come a long way over the years and I believe every shop should have some. I would like to point out the there is an error on your matrix. The Quest SQL server (Spotlight is it's name) does monitor/alert/advice on Windows OS and networking. I have been using this product for 10 years now and have also evaluated most of the other products. It seems that time and time again it works the best and no I do not work and/or get kick backs from Quest. Every DBA / Developer I have shown this product to purchase it. It just works that well.
There is a enterprise version that will colllect information/stats from all your SQL servers (including Windows and network stats) and stores them into a centralized database. From that you can use and/or create customized reports it get everything you ever wanted to know. We have used this product to help determine which SQL servers would best operate in a consolidated server, meaning a server with several instances of SQL server installed.
To all the readers, take my advice and get some tools. It really make life a lot easier.