Convenience comes at a high premium. That is how things are now valued. Real estate that is closer to amenities comes at a higher price than much larger real estate further from those amenities; automobiles with more luxury items come at a higher cost that those with a standard package.
Yes, value is based on convenience. Before elevators it was less convenient to live in the upper level penthouses because of the time and energy that it took to walk up the stairs to the apartment. Now that elevators have been invented, the upper level apartments offer a better view and are convenient to get to.
No, convenience is only a small part of determining real estate value. This value incorporates important concepts of consumer demand, accessibility and the general condition of property. Crime, pollution and fire safety issues also impact value in many apartments, helping to set the amount of rent reasonably asked for a property.
Real estate value is not just based on convenience--there are a number of factors that contribute to a property's value. The penthouse has become popular because of the great views afforded to residents that live at the top of a building. Modern elevators and building construction have improved the quality of penthouses. That's why they are so popular today.