Should you use the same tiles in all the wet areas of the house even if the rooms don't meet each other?
The current trend in house design is very much 'open-plan' with colours and finishes similar throughout. Where the space is divided by walls or rooms, the idea is to maintain flow through your home by extending the finishes and colours into these new rooms.
I would definitely use the same floor tiles and wall tiles in all the wet areas throughout your home. Even with the rooms not meeting each other, the use of the same tiles maintains this flow. Even down to the feature tiles, if used. Some might think that feature tiles within the toilet and laundry is a little 'decadent' but these small details all help to maintain the flow throughout your home.
To achieve this is a lot easier if you are building a new home. Although check with your builder as most do have a specification on the tiling for the wet areas and this might need to be changed.
If renovating you might also need to include the cost of removing any existing tiles when working out your budget.
If you are after a more traditional look, then still use the same tiles in the wet areas but not necessarily the same tiles as in the rest of the house.