It's just a different type of meeting - I generally find them more relaxing and it's nice to let someone else do all the work occasionally.
Sometimes I like a rub and tug because I can't be arsed with sex, or I'm hungover. Sometimes they do actually give you a reasonable massage, particularly the Thai girls. Most of them have got pretty good at giving handjobs as well, generally much better than a normal escort would give.
If you see the same one two or three times then extra services might become available too, although that's not the main reason to see them over a standard WG, just a nice bonus when it happens.
I should also add that I definitely wouldn't expect to spend the same amount on a massage meeting as a normal meeting - I agree that paying a standard WG rate for a rub and tug is a bit ridiculous.
