Well....I come from a family of "check grabbers", LOL. So although technically the person who hosts/arranges the meal pays, in reality six different people are grabbing at the waitress/waiter!
We try now to make it clear when it's a "everybody pays for their own meal" situation, at least for family.
Since we know way too many poor people - perhaps not so much poor, but we know they're sometimes skating a tough edge financially - in that situation, if we've offered the invite, we make it clear we're paying.
I actually don't like letting someone else pay the tip, because we tend to be generous in tipping when we've gotten very good service. Most people will not tip more 20%; my in-laws used to only tip 15%! Since my mother was a waitress for a number of years - and my DH worked as one while he was going to culinary school - I know how hard a job it is, and how much the waitstaff depends on tips.
Our best friends are a younger couple. The wife is the more pragmatic; she doesn't worry about our picking up the check because she knows we do what we can afford, and if we couldn't afford it we wouldn't do it at all. The husband can't help feeling guilty because she's more a "you treated us last time, so it's our turn to treat you."
We compromised by agreeing that they can pick up lunches, and we'll pick up the dinner tabs. Works out fine.
Life's way much shorter at this stage in life.