technically your urls ARE also hardcoded too. you just hardcode a relative url and assume that the images will be in '/images/yourstyle/xxx.gif'
first thing i did was to modify your urls to '/styles/yourstyle/images/xxx.gif', because i believe it's more logical there at least.
and the person installing the style will still have to know to ftp the images appropriately to the 'relative URL'
way i see it is that it's 6 of one and 1/2 dozen of other here. i see just a difference of full vs relative and that's it.
neither is 100% automatic

now if the style uploader itself took that into account and the images magically appeared all synced up.... hrm.. now where did i hear that before? *crickets*
it's like deja vu all over again...

ps: allen, i used your theme and it turned into one of the more popular ones, btw