I believe that is basically it. They won't be participating in writing specifications, but I don't think that anyone will be stopping Apache (or anyone else) from implementing any of the JSRs.

If a hypothetical Java Servlet API v4.0 would be released they could still make Tomcat be compliant with it.

On the other hand Tomcat is very widely used in the not-quite-huge-enterprise companies and it is obviously helpful for a spec if all implementers can agree on some common ground before it is written. ECMA probably wouldn't see a point in doing ES5 if Microsoft and Mozilla would not talk to them.