escape velocity varies with altitude/distance from earth. it's the speed needed to escape the gravitational force of a body without propulsion (and has little, if anything, to do with getting into orbit). for example, if you threw a baseball straight up at a speed of 11.2 km/s from the ground, it would escape earth's gravitational pull (theroetically of course, not accounting for air resistance, which would make this feat impossible). however, at 9000km altitude, the speed needed for the baseball to escape is 7.1 km/s
numbers taken from
http://en.wikipedia.org/wiki/Escape_velocity
escape velocity is not about constant speed with propulsion. sure, with constant propulsion, at 10 km/h you could go and go and go. you could do the same at a .0001 km/h. it's about the momentum of the object against the gravitational pull of another object.
another explanation:
http://www.physlink.com/education/askexperts/ae158.cfm
"If you throw an object straight up, it will rise until the the negative acceleration of gravity stops it, then returns it to Earth. Gravity's force diminishes as distance from the center of the Earth increases, however. So if you can throw the object with enough initial upward velocity so that gravity's decreasing force can never quite slow it to a complete stop, its decreasing velocity can always be just high enough to overcome gravity's pull. The initial velocity needed to achieve that condition is called escape velocity."
so, ignoring air friction, escape velocity is around 25,000 mph (you were close!). however, astronauts travelling to the Moon or Mars would be concerned with the escape velocity from above the atmosphere, as no craft is going to go 25,000 mph within it. (the space shuttle re-enters the atmosphere at 15,000 mph and glows red hot!)