The RosettaNet CEO delivered an excellent presentation on this topic a while back, the slides can be found at: http://xml.coverpages.org/rosettanetPerspective.ppt. This presentation covers in detail what a universal B2B standard should look like, where RosettaNet stands, and where the other standards are.
I'll offer another perspective. EbXML and Web services specifications allow an organization to create business processes. While Web services are ideally suited for composing processes within the organization, ebXML enables a business-to-business collaboration framework. While ebXML and (to some degree) Web services specifications create the ability to express business processes, RosettaNet uses these business process expression languages (RosettaNet has adopted the ebXML's Business Process Specification Schema, BPSS), to express the standardized business processes.
Yet another way to look at the differences between ebXML, RosettaNet and Web services etc, is to look at these specifications as being "horizontal", or "vertical". A horizontal e-business standard is a set of specifications that are common to all e-businesses, while a vertical e-business standard focuses on a particular ability or a particular business area. For example, ebXML is a horizontal standard, and RosettaNet is a vertical standard. While ebXML provides an infrastructure to create standards (Web services specifications are not ideal for creating B2B standards, but they can also be considered as horizontal in nature), RosettaNet focuses on specific industries (e.g. Semiconductor manufacturers, Computer manufacturers etc) and creates standard e-business processes in that "vertical" space.
Theoretically, RosettaNet could be based on a horizontal standard like ebXML, and a lot of effort is currently underway at RosettaNet to use ebXML as the base. For example, the BPSS will be used to express RosettaNet PIPs (partner interface processes, a.k.a. business processes), the ebMS (the ebXML messaging service) will also be adopted at some stage, replacing the RosettaNet Implementation Framework (RNIF). There are also some rumors that RosettaNet will adopt the ebXML registry/repository as a base for a new RosettaNet initiative (RosettaNet Services Model).
Theoretically, BPEL4WS could be used by RosettaNet to express the PIPs as well. Realistically however, BPEL4WS is not sufficient to express robust B2B collaborations and more suited for use inside the enterprise.
So where are RosettaNet standards used? RosettaNet is currently in use particularly in supply chain situations, for automating interactions between the business partners within the supply chain. However, as RosettaNet has standardized common business processes, a lot of them end up being common to all sorts of business, and you can find RosettaNet specifications being used in all sorts of e-business interactions.