I totally understand the authors sentiments and I don't think he's being a stick in the mud. I hate this sort of setup because inevitably someone orders the most expensive meal, or several expensive drinks, or a couple of bottles of wine and expensive appetizers and then the whole group is supposed to split the check evenly! I've been to dinners where the amount of food and drinks I've had would have totaled less than $30 after tax and tip, but I've been asked to chip in upwards of $75 because everyone wants to split the check (at times I have successfully protested, but it's really a terrible position to be in). I hardly think that not wanting to pay more than double the price of what you've actually consumed makes you a stick in the mud.
I've stopped attending this types of parties, because on top of the problems the author describes, there is also the issue of some people not putting in enough money so that others have to pick up the slack. The whole thing is just terrible.
I am of the belief that birthday parties should be paid for by the host. If the host cannot afford to pay for everyone's dinner, then they shouldn't have a birthday party at a restaurant. I also dislike when people say, "in my group of friends it's accepted" because I'm sure my friends think it's accepted too, but I know I don't like it and I know other friends don't either.