Since when did privacy become synonymous with secrecy?
It seems a little exploitative to say that this girlfriend, the secondary, should sacrafice her own sense of comfort, her boundaries and privacy just for the "intimacy" of a relationship she isn't even involved in. Why is the OPs need for detail and the security she finds in discussing the sex life of her husband and his Gf more valid or important than the gfs desire for some discretion?
There is nothing wrong with sharing intimate details of your sex life or asking questions of others...but there is also nothing wrong with NOT asking or telling. It really is preference. No one should be judged based on their preference.
I personally wouldn't want a partner to share information or details of my sex life and I am not the least bit ashamed. I am a classy girl...and I don't fuck people so that someone else can enjoy the story later. Also, it takes away the intimacy...might as well tape it.