On the page... http://tomcat.apache.org/tomcat-6.0-doc/config/http.html ...the maxKeepAliveRequests description is only in the "Standard Implementation" section. However, since it's applicable for the NIO implementation, it would appear that it properly belongs in the "Common Attributes" section.
Common attributes are only those required by the org.apache.catalina.connector.Connector class Whilst some additional attributes are supported by multiple connectors, these should be listed individually against each connector. I have added maxKeepAliveRequests to the NIO connector for trunk and 6.0.x. This will be included in 6.0.19 onwards.