R/3 Enterprise on Web AS 6.40

Does anyone know if R/3 Enterprise will run on Web AS 6.40. I just heard a presentation where we informed that only Web AS 6.20 or 6.30 was compatible. However, I thought the Web AS was downward compatible. Also, 6.40 is in ramp-up right now, if it can't be used for Enterprise, what is the ramp-up for? I can't see that SAP would expect customers to run NetWeaver components on 6.40 and then have a separate Web AS for Enterprise. These are very confusing times.