If you invite me round for dinner - and you should, I'm a fucking excellent guest. I will bring wine... usually at least one bottle, probably two. That's what I contribute. So I would argue the costs are defrayed accordingly in a restaurant. If I was feeling argumentative I'd also argue the costs of the wine are often equal to the value of the meal in broad brush costings... though not the paid labour required to cook the meal.

So, whoever invites should pay - but not offering to pay for drinks/half/make a contribution should be viewed as a similar affront to showing up empty handed at a dinner party. If you did that, and I knew you were rich enough to purchase wine on the way over then I reserve the right not to host you ever again.