Today, I tried to update the maps on my TomTom device with a road map of Iceland. For that I navigated to the online shop.
Unfortunately, I couldn't find there any road map from Iceland. On the other hand there are maps of the Canary Islands, and other remote areas, but not Iceland.
I don't know why there are no road maps of Iceland - but to answer the implied question of other ways of getting Iceland maps the following may be helpful.
When I've needed navigation data for Iceland I've used Open Street Map, on a Garmin device. It looks like it should be possible to get them to work on a TomTom for more details see the TomTom page on the OpenStreetMap site. I've got no experience using them on TomToms so I'm afraid I can't offer any more advice on how to set it up.
UPDATE: TomTom now have maps for Iceland. As of their latest update, this has been added to the 'Western Europe' collection for many devices.
TomTom use "TeleAtlas" maps, and in fact they actually bought TeleAtlas several years ago.
As with most mapping companies, TeleAtlas has varying levels of coverage for different countries. For countries like the US, TeleAtlas has near 100% coverage, which is to say that they have not just major highways, but all the way down to minor streets and even (in some cases) dirt roads and the like.
For some countries, they only have "major road" support, so they have highways and some major metropolitan roads, but little else. These countries include places like Mexico and South American countries, and much of Central/Eastern Europe.
Iceland has always been a strange case, in that TeleAtlas have never had any coverage of it. I can only presume this is a business decision in that they have decided it's not worth the money/effort to create such maps, and I'm not aware that any official reason has been given.
Other GPS manufacturers use different maps. eg, Garmin use maps from Navteq in much of the world, and Navteq do have maps for Iceland - thus so does Garmin.
Currently there is no way to load maps from any other sources onto TomTom devices, so your only option is to either buy/rent another brand such as Garmin, use a paper map (remember them?), or perhaps just get lost (which can often be lots of fun!)
Although other answers are valid, the driving reason is that there isn't the demand. Iceland has a population of around 350,000, and had around half a million tourists visit (figures for 2007). The Canary islands have a population of more than 2 million and 9 million tourists visited.
