Lately I am seeing quite a few application development job ads asking for experience with this or that Java EE server. I can understand this if it is for a server administrator, however I find it stupid and ridiculous to ask for some one with a specific server implementation experience when the job is Java software development. The whole idea behind Java EE as I studied in my initial days was for development of standards and to deploy to any platform of choice that including servers, OS, etc.
My question is, are the various Java EE application container implementations so vastly different that they can be considered their own career path for development? What kinds of features exist amongst Java application containers that require such specialized skill that I might not want to not consider applicants with otherwise impressive software development qualifications?