indeed. I'm not sure how much the website takes into accont the Thames flood defences either.
I don't think they do at all. For example I'm pretty sure the Netherlands will be ok, regardless of sea level rise (unless it's really massive, like 10+ meters), because of their defenses.
In other places though, where there are sand beaches for example, that's not an option, unless they are willing to abandon the beaches; and in other places again, they don't have the means to build adequate defenses (you feel sorry for the thousand people who died in that factory collapse in Bangladesh? See how many people there would be affected by a sea level rise of 5 metres...).