Where did you get this "little gem" on HBO content?
"Most time" is a bit of a stretch. 90% of Hollywood movies are going to be the same on HBO and Cinemax.
I doubt HBO actually "edits" anything. However, if there is an "unrated"/NC-17/directors cut of a movie- which is common with comedies these days- HBO will always show the R-rated theatrical version while Cinemax may or may not show the unrated version.
I assume that Hemi is talking about the softcore porn on Cinemax. But HBO generally doesn't show these movies at all, except on HBO Zone. I'm not sure if there are any differences in the explicitness
I know for a fact that Showtime has contracts with cable companies that prevent them from showing NC-17 films. I believe HBO does the same...perhaps just keeping HBO Zone off those systems.
Generally speaking, Starz is the "cleanest" service, partially because they carry a lot of Disney content. They used to actually show edited versions of R-rated films in the daytime, but stopped that long ago. For a while, Starz Edge showed some tame softcore porn, but I think they have stopped that. Starz Cinema does not shy away from more adult-oriented art-movies (for example, "Karma Sutra"), but it's not a regular thing . The Encore channels may even be a bit cleaner. Neither service carries hardcore horror films either...nothing stronger than a typical hollywood r-rated release. But neither service "edits" anything, they just don't show much overly explicit programming.
HBO would be next. HBO does not even show R-rated programming before 8pm. They do have some explicit original programming, but shy away from outright softcore porn, except for Zone. Just like Starz, there is very little "b-movie" programming on HBO.
Showtime is next up the ladder...they do show a lot of soft porn, but in general, they are more "erotic thrillers", and they would probably all get R-ratings with no problem. They do show a lot of b-grade horror films, especially on Showtime Beyond, but nothing too extreme.
The Movie Channel and Cinemax are the most explicit. Cinemax is know for it's "skinamax" programming, and they are not much different that what used to be shown on the old Spice channel. The Movie Channel shows similar barely-soft porn movies, as well as some pretty graphic horror films.
Oddly, IFC is probably the most explicit channel of all at times, yet it's carried on basic tiers. Turner Classic Movies will also sometimes show films-mainly on their TCM Underground block- that HBO might shy away from.
EDIT- HBO DID have a service in the 80's that was aimed at families who wouldn't buy a service with more explicit programming. It was called Festival, and I think it may have edited films. I think there was another one called Home Theater Network. They both died off...there's just no market for premium channels that actively edit their programs.