St. Charles County is most certainly exurbia, and there is no indication that it will change its voting behavior anytime soon. The St. Louis metro area is generally not an area that has attracted the white collar liberal, and a large portion of the white Democratic vote come from the white working class. St. Louis does not equal Chicago. Yes, there are small patches of more moderate suburbia in older suburbs like Clayton, but most of the increase of the Democratic vote in St. Louis county is due to a higher percentage of the population being black compared to what it was in years past. The 2nd congressional districts boundires have generally followed the path of "white flight" from St Louis to past St. Charles.
If one looks at the St. Louis Metro area, they will notice that working class Jefferson County, South of St. Louis, a county that is 98% white went for Gore in 2000, and Jefferson County is about as far a place as one can imagine being a yuppie haven. It is a county that has a large number of unionsed workers.
That said, with a large amount of growth in St. Charles County, KC suburbs like Independence MO and especially Springfeild, the Dems will have a togher time in MO than in years past.
Great analysis of the St. Louis area. St. Charles County is heavily GOP. I am actually from Jefferson County, and can report that while it remains Democrat leaning, it is becoming less so as it grows. The median home price out there has been going up with massive new developement, and the new people are much more likely to vote Republican than the old. Btw, I hate that place.