Using currency exchange rate is not a good way to determine where food is cheaper. You should be looking at purchasing power within countries. Exchnage rate is determined by money market, and may mislead you. If I make 2K Euros a month in Italy, and a friend of mine makes 2k $ in the US, given current exchange rate you may assume that I make more, which may not at all be true if goods costing 1 $ in the US cost 2 Euro here - as it often happnes, being esxchange rate unrelated to that to a large extent.

To go back to tipping, I am really not usre that tip culture has an impact on cost of food. On the other end, personally I think it is indee possible that it does cause low wages for waitstaff. Clearly, as a waiter you'll be willing to accept a lower wage if you know customers will tip a lot. BAsically, tipping alters the labor market. I don't say it is necessarily bad, but travelling would be easier if tip culture did not vary so much from country to country.