There are parts removed from Pure Effect in the later editions. Why, I don't know...
Absolute Magic is unchanged in it's various additions, although Derren does say he was tempted - just to piss people off I guess.

If you're desperate to get hold of Pure Effect for it's magical contents then most of it is covered in Devil's Picturebook which you can still buy from his website for a much more reasonable price. But then you'd be missing out on Derren's brilliant poetic bitching, they are the best reads of any magic texts out there!