Not all providers say that fizzy drinks are not allowed. My own advises that they cannot be had during the first two weeks post op, but they aren't a "banned" food item at all - but then, they work on the philosophy that there are no "banned items" and that a lot of it boils down to individuals tolerance of the foods/drinks themselves. So to say that they are a complete no-no and that they cannot be had for life, isn't correct. But this is something down to your provider, what surgery you have and what they advise.
I used to drink litres of the stuff on a daily basis - I've had maybe 1 or 2 small glasses a month since my surgery, but I find that it doesnt quench my thirst and cos Im drinking 2-3 litres of water a day, I don't really feel like it, but I am, with my provider, allowed to drink it.