I think the problem is that no one ever explained to the server they need to bring change back in a manner that makes tipping easy. It is like one of those things that people KNOW, but they don't explain. I remember my dad explaining this to me when I was a child - when you get change at a restaurant, the waiter will always bring back bills that make it easy to tip. If you don't need change, tell the server when you hand over the money. I feel confident that the waiters we dealt with way back then would have brought change as the OP is expecting. I find a lot of things that my parents taught me are no longer common knowledge.
On the flip side, maybe the servers were hoping for $10 as the tip. I used know a pizza delivery guy who would do that - if someone handed him $40 for a $30 order, he would say thanks and start leaving, making them ask for change. I guess that worked as a one-time strategy, but it probably didn't pay off for repeat business.
On the soda-to-go - I had never seen this before maybe 2 years ago, but it has become common in this area since then.