Yes for FREE for those who are not known to be an escrow, they want to make a name for being an escrow and for feedback. That's why there's a list of trusted escrow to chose from and not go from those who are new. At least give them something for their time and effort.
That isn't completely true. There are quite a few escrow providers who are already highly trusted and offer free escrow services (SebastianJu, for example). Of course it's appreciated to tip an escrow provider but lots of the escrow providers around here escrow deals for free to prevent scams. If it takes them 30 minutes to prevent someone from being scammed a few hundred bucks, they're happy with that.