My guess is that they are because ISPs may keep records of them—I think they are required to in some jurisdictions. But you don't have to store IPs in your server logs.
You're also allowed to store IP addresses in your logs, you just have to take care with the data and the reason you're storing them needs to be justified - either because you have a legitimate interest in doing so (e.g. security) or because you have my explicit consent.
If I order something from an online shop, they don't need to have a banner in order to take my name and address to post the item to me - that's fully expected and reasonable. They do need my consent if they want to use that to post adverts to me though.
