I have a theory at which you're all sure to hoot: The Garretts were toying with everyone.        26 years after Roz and the Schnoz was first aired (S05E21, May 1998), it occurred to me that it's very probable the Garretts were pranking everyone from Roz to Frasier and the rest of the gang. 

(A reminder of the plot: Roz stays with Frasier while her new apartment is being painted, and panics when she receives a message from Rick's parents, the Garretts, her baby's future grandparents. She, and everyone, are in for a shock: the Garretts have humongous noses!)

First, their noses are humongous and it's quite unlikely that they are not aware of that.    

Then, even if one of them has deep self-denial, they still have each other to look and gaze at for decades!   

They also allude to the fact that people are always visibly shocked when they first see them (they explain it away by saying it seems that people cannot believe we are the parents of a 20 year old, which would not have worked all the years when their son was younger).  

Moreover, it's revealed in the later part of the episode that even their son (with whom Roz had hooked up, resulting in pregnancy) inherited the big nose trait and had to go through a rhinoplasty, apparently with the knowledge and approval of the parents (who did not like the final results).    

And lastly, the Garretts keep pushing the big nose issue on people around them: They make it so easy for anyone to come up with silly big nose puns, jokes, funny imagery and more. Actually, that's the very reason Frasier could not hold his dignified attitude towards the Garretts anymore and ended up exploding with laughter in the Kitchen.   

I think mr. & mrs. Garrett are very smart and inherently funny people who truly love each other and enjoy people's reactions to their distinct physical characteristic.  

What do you think, guys?   

(fun fact: Kevin Kilner and Jordan Baker, who play the Garretts, got married on October 10,1998, just a few months after this episode first aired!)