I think what they meant is updates to 3.2.1 GA are not supported with configurations using a combination of CLX and RC today, other remote copy configurations are fine, this is likely to be a CLX qualification issue (identifying corner cases is what the controlled release is all about). But yes you are correct the two are used together otherwise there's no point running CLX. Peer Persistence is now supported on Windows clusters / HyperV as well as VMware as part of the Remote Copy suite so the use case for CLX is likely to be reduced moving forward.
I think they were maybe a little too precise in the wording which led to the confusion.
Express writes are part of the Inform Base O/S in 3.2.1 it's an optimal method of posting writes on the array HBA to reduce latency per write, very important for flash systems where low latency is king. There's a great video that Ivan Iannacone did which discusses express writes among other things.
http://h30507.www3.hp.com/t5/Around-the ... CmIR_ldXg0