While I'm not sure if it's a regular thing or not, you have to consider that there are different rules for DVDs and internet distribution.

With DVDs, retailers can be sued if a certain DVD contains scenes that would be considered violating community standards, so many retailers opt not to distribute such DVDs (hence the studios don't put out DVDs which contain material that could lead to retailers avoiding that product).

With online scenes, there are no retailers in-between, so everything goes (as long as the credit card companies play along)

Things on the no-no list: fisting, pee, (simulated) rape & more...

I'm not sure about the scenes you mention what is missing there.

Also, I'm not sure if scenes are simply cut for run time, because the studio doesn't want to put out a DVD with two 90 minutes scenes (and people complain about too few scenes), but instead opts for three 60 minutes or four 45 minutes scenes.

[Link]

I can confirm the missing 10 minutes on the Stepsisters share everything.

The cover at the end says total runtime 3h45m, but the runtime (movie plus bonus scene) is 2h49m+40m = 3h29m

And the cut really doesn't make any sense... must be a mastering error, but apparently nobody cares anymore for proper DVD mastering.

[Link]