What a brilliant question! I always think it is so important never to look at these tales in isolation but to consider how the stories and the conversations between the characters that intersperse them relate to the overall work of literature.
Clearly, there are several ways in which we can analyse the "conversation" that is really going on through the tales. Let us remember that the Reeve himself used to be a carpenter and is now getting older. The character of the aging carpenter who is cheated in "The Miller's Tale" can thus be seen as a comment on the Reeve. The way in which the Reeve takes the Miller's Tale personally is shown by his desire to get back at the Miller through his own tale in the Prologue:
This drunken miller has just told us here
abotu the diddling of a carpenter;
As I'm one, it's to scoff at me, perhaps.
If you don't mind, I mean to pay him out;
It's his own loutish language that I'll speak.
I hope to God he goes and breaks his neck.
Though he can easily see a mote in mine,
In his own eye he cannot see the beam.
The tales of these two ribald characters are therefore clearly a way of advancing a personal argument between them. Both tales have as a central character a miller and a carpenter, and both of these characters deliberately satirises the enemy of the storyteller. In both of these tales, the miller and the carpenter are shown to be tricked and deceived and are victims of their own greed and jealousy. The tales are therefore means of publicly ridiculing and making fun of each other.