Well, there is a lot of porn out there, and it certainly isn't 'all the same'! Wonder what some of the ladies would do if a PSE booking turned out to be made by some guy out at the freakier end of the porn spectrum, expecting something rather more outrageous than they might be thinking!
I think the WG's use that term to advertise a raunchier level of service than what is probably advertised as a 'GFE'. I wouldn't just use anal as being the difference between the two variants.
I've visited Naughtyaimyxxx twice and the first time was much raunchier than the second time - perhaps because I specifically requested 'PSE' the first time. I assumed it would be the same, next time, but it wasn't quite so full-on.
In my mind - I think if you watch some of the stuff like brazzers in porn, those kind of scenes are probably what 'PSE' is meant to represent - it's not bizarre but it's normally a bit more full-on than some of the more 'romantic' scenes.