What would be interesting to know is if Mr Pratchett has read the Moomin books, which of course is very likely.
It is strange that I did not notice the likeness before, since I almost know the Moominbooks by heart, but I would put that down to the narrative force of the Discworld itself, that might have obscured my observation.
For those of you who have not met the Moomins there is a nice little corner of reality to explore. It is certainly not as grand or detailed as the DW, rather homely one could say, more like Shire in ambience, but is has a certain charm and whimsiness that is most enchanting. (One of the characters in the original Moomin comics - beware of all japanese and other versions - is an old friend of Moominpappa, called Wimsy. He usually sleeps under the dinner table when visiting the Moomins.)
But watch out! I do not know anything about the Moomin publishing history abroad, but it is necessary to check from which edition they are translated. I am sorry to say that the author herself, Tove Jansson, has made several revisions of the Moomin books, none of which are to the better. Thus the earlier the edition from which it is translated, the more of the original uniqueness is preserved.
I actually stumbled upon this English translation of Comet in Moominland about a year ago, and yes, it is made from the -46 edition. To my delight it contained material that was not in the Swedish -51 edition (they were written in Swedish) which I read as a child. This also proves my point about the revisions.