Liferay replaces the servlet container's filter matching rules with those held by the InvokerFilter if web.xml is at least version 2.4. However, if web.xml is <= v2.3, the filter regexes are not managed.
This is a relatively minor issue since most plugins should have their web.xml at least at version 2.4. If they are not, they should be upgraded to version 2.4.
However, for complete safety, we should warn the developers that they need to update the web.xml and also should provide some minimum capabilities to apply regex.