Can anyone think of any reason checking the ignition would cause my Miles to Empty calc to get screwed up?

I just picked my car up and on the way home (20 miles) my MTE has not budged from 187. Is that based on a float in the gas tank? Maybe something got stuck when it was up on the lift?

 

If the sales guys were hammering your car, the expected miles to empty is low. If you drive sensibly, the miles to empty will get better. You may be at a point were you are getting better and better MPG and thus even though you are travelling miles, the distance to empty is the same. If everything is working, the miles to empty will go down soon.