Sorry, they are considerably more expensive than a storage tank heater. Especially in a retrofit situation, but even in new construction.
How often exactly to you drain your storage heater? Excluding vacation homes (where all the plumbing would need to be drained) the only time I've ever done it is when I replaced a 20 year old unit.
I've never had to replace one.
Modern storage tank heaters are glass lined and self cleaning. If you don't get a minimum of 20 years use out of one, you aren't trying.
WTF???? If you are changing anodes on a residential water heater, you have far more problems with the rest of your household plumbing that you need to be worrying about.
You don't really have any experience with tankless heaters, do you?
No, in Europe they have a lot of older housing stock with construction that makes it difficult to run insulated hot water lines. There are other factors that come into play as well.
Most of the new residential housing I've seen in the UK uses storage tanks. Here's an example:
Go down to the plumbing section and note the words: "Each apartment includes an insulated hot water cylinder, with electric emersion heater back-up." A Google search on "hot water cylinder" will yield many other references.
And if you would like some factual information, you can download this study:
The bottom line is that except for a few specific circumstances, storage tank heaters are cheaper to install and operate over a given period of time than tankless.