Same exact site on 2 different domains???

i'm on the list of a marketer that's doing something interesting. he has 2 sites that are exactly the same, one on a .net and the other on a .com. the only real difference between the two from the visitor's perspective is that all the links on each correspond to its domain, there's no cross-referencing. for example, nowhere on the .net site is there a .com link, and vice versa.

here's where it gets interesting. both the homepages on each domain have an opt-in and once u get on the list from either domain all emails come via a .net address, yet the links in the emails are all .com, even the unsubscribe. furthermore, the .net cannot be found on a G search, but can be found typed directly into the address bar. it's as if he did something like a "noindex" or used the url removal tool, not sure.

my only guess is that he wants to protect the .com from spam complaints, etc, and so email markets via .net. does this sound likely? also, how easy is it to continually update both sites so that they're identical, would he be updating one site and then copying the whole thing and uploading it to the other domain?

not sure what's going on exactly. what makes me even more curious is that this is one of the most prominent products from one of the most prominent marketers, nearly everyone in im knows of him. the only reason i didn't mention his name or the site is because i really don't want to out him.