The style of the controls is determined by the designer who made the jplayer skin (ie blue monday). One can override it with more css or copy it and modify it to make a new skin.
I'm a developer not a designer so I include what is available and leave it to others if they want to change it but designing new skins for jplayer or modifying ones they provide is not something I'm inclined to work on. I have a huge list of things to do that are more of a priority for me.
In this case some artisteer css was interfering with the css of the jplayer skins and I added some css to cancel out what artisteer was doing so it would not affect the jplayer style.
If others want to contribute new skins for jplayer that would be fine with me but it isn't something on my to do list and doesn't hold much interest for me.