I live in Boulder, Colorado which has a fairly high COL. We moved here from a town of 10K in Iowa. We have a tight budget on an income that would give us more wiggle room in many parts of the country.
Practical reasons we are here:
Real Estate continues to be strong. While not what it was at one point, because of caps on new construction within the city limits, our house continues to appreciate at a decent rate.
We have a chiropractic practice that continues to grow despite the recession. We've reduced our fees but by and large, people here can still afford to pay out of pocket or barter. If we were to move to a low COL state, we'd have to start from scratch in a place where folks probably couldn't afford our fees.
That said, both DH and I have 2nd jobs to supplement. He writes and I work part time for a chiropractic organization. Still, we both work less than 40 hours a week.
We function quite well with one car.
Which leads me to the less practical but equally important reasons we live here.
More sunny days than Honolulu or Miami.

We enjoy an active, outdoor lifestyle.
We have lots of choices for schools.
Liberal politics.
Strong support for a local living economy...Boulder residents overwhelmingly let WalMart know they would not be supported here.
Strong support for treading lightly on the earth.
Thanks to college students and our extremely affluent neighbors, we have amazing garage sales and heaps of second hand stores with incredible clothing...one can live well and frugally here.
Strong social and political activism.
Lots and lots of small organic farms.