My take of high-maintenance means that the other person in the relationship has to use a lot of time and energy to keep the person happy. The high-maintenance people are unable to find the happiness and assurance within them as Maleficent said. They have many issues and are unable to think or do for themselves and would rather have someone else 'save' them and pick up the pieces. This can be brought on by insecurity or helplessness.
However, I don't think that the outward appearance is high-maintenance to anyone else, but the person who is getting themselves ready. The partner in the high-maintenance relationship doesn't have to put the make-up on the person or dress them. That is a different type of maintenance that is personally chosen by a person and doesn't necessary make or break the relationship as the first type of high-maintenance. People choose how they want to look to other people. Although the woman in make-up, manicured nails, and designer outfits look high-maintenance, it may also just be that they want to put their best foot forward and by dressing like that, that is how they do it. I'm not saying that the opposite of that is bad either, both ways are a choice and neither one is wrong or right.
However, the outward appearance high-maintenance can become an issue if the woman (or man) is constantly wanting positive feedback to know if it's 'working' or not. Especially, if the person is also a pleaser on top of being high-maintenance.
Either way, I don't think a relationship should be that hard and if I saw someone that was high-maintenance in the first description...well that's too much drama and work for me. But then again, maybe they want someone to put their foot down and make them do things on their own. I don't know..people are complex. I just know that I fell head over heels for the first guy that didn't treat me like a princess and put me on a pedastal and now we're happily married.