I have found two differences in jars files for RESTEasy x EWS.

RESTEASY:
jaxb-impl.jar
935473 bytes
520934923deda6eb79ae279b3defd581 jboss-ewp-5.0/resteasy/lib/jaxb-impl.jar

Manifest-Version: 1.0
Specification-Title: Java Architecture for XML Binding
Specification-Version: 2.1
Ant-Version: Apache Ant 1.7.1
Implementation-Title: JAXB Reference Implementation
Implementation-Version: 2.1.9
Implementation-Version: 2.1.9-04/02/2010 11:24 AM(mockbuild)-fcs

EWS:
jaxb-impl.jar
912525 bytes
450fe788de11854d5c00630283f141ce jboss-ewp-5.0/jboss-as-web/client/jaxb-impl.jar

Manifest-Version: 1.0
Specification-Title: Java Architecture for XML Binding
Specification-Version: 2.1
Ant-Version: Apache Ant 1.7.1
Implementation-Title: JAXB Reference Implementation
Implementation-Version: 2.1.9
Implementation-Version: 2.1.9-01/26/2010 04:37 PM(mockbuild)-fcs
###############################################################
RESTEasy:
jettison.jar
72530 bytes
08843778c4f2a6d05aef0400383b291d jboss-ewp-5.0/resteasy/lib/jettison.jar

Manifest-Version: 1.0
Ant-Version: Apache Ant 1.7.1
??

EWS:
jettison.jar
70188 bytes
9d8d20f1f54fd7634eee23b825214450 jboss-ewp-5.0/jboss-as-web/client/jettison.jar

Manifest-Version: 1.0
Specification-Title: JBoss
Ant-Version: Apache Ant 1.7.1
Implementation-Title: JBoss [EWP]
Specification-Version: 5.0.1
Implementation-Version: 5.0.1 (build: SVNTag=JBPAPP_5_0_1 date=2010042