Wizard Wear/Wizarding culture

[Steve Vander Ark]

No: HPFGUIDX 9160

re: what Molly and Arthur wear on their trips to Kings Cross:

When I first read HP, I assumed that the robes they wore were INSTEAD 
of any kind of Muggle clothing. I still read it that way, especially 
in light of Archie's fondness for breeze under his robes and Herry 
and Ron asking Hermione to leave the railway compartment so they 
could change. But the pictures we've seen--the GrandPre drawings, the 
commercial/calendar art, and the pictures from the film set--often 
show robes OVER pants and a shirt or other Muggle clothes. I think 
that visually this just works a lot better in many cases. So if we 
take the pictures as an indication (yes, I know they aren't canon) we 
might assume that witches and wizards dress in clothing similar to 
Muggle clothing with a robe over. The Muggle-ish clothing wizards 
wear is brighter in color and of a very different style, probably, 
such as Fudge's bottle-green suit or the folks Vernon saw on his way 
to work, but passable. It might draw glances, in other words, but 
still be just within the range of normal to a Muggle. So what about 
Archie? I'd say that many wizarding folk do dress in nothing but 
robes, especially those who have no dealings with the Muggle world. 

This does make some sense too if you look at Wizarding culture in its 
entirety. It is essentially a medieval culture, based on a medieval 
world-life view. That's when magic still held credence in our 
civilization. The Renaissance scrubbed our minds of that nonsense and 
replaced it with good, solid, experimetnally provable science. This 
hasn't happened to our counterparts in the Wizarding World, however. 
They are still in the middle ages in many ways, although they do have 
many of the trappings of modern society, copied and made to work not 
with technology and science but with magic spells. Like the Knight 
Bus and the Wizarding Wireless, these things do not fit exactly or 
work the same. They are copies based on what they see to meet the 
same basic needs of society--mass trasit, mass communications--
although they do not understand the scientific concepts behind the 
Muggle things they copy. The Knight Bus carries passengers like a bus 
but does so not with a gasoline-powered engine but with magic, and 
the trees and houses jump out of the way.

Steve Vander Ark
The Harry Potter Lexicon
which should probably have a page talking about this...hmmm...
http://www.i2k.com/~svderark/lexicon