Unique styles and looks are very hard to do. There are many reasons for this, but the two main reasons are: it's hard to be original; and there's only so many ways to draw a particular widget. While these may seem like nonsense, once you start creating a new style, you'll run into these problems more often than you would expect.
I am in the middle of creating a new style that I intended to be completely original, but now that it's almost done, I can see that some QNX and NeXT influences have crept in subconsciously. In the meantime, if you want something that doesn't leap out and scream Windows or Macintosh, check out Qinx or Alloy as two non-standard themes available on kde-look.
"and why can't KDE do bitmap themes?"
Because "theme-engines" are so much better! KDE can do bitmap themes (the standard SGI and Marble themes are bitmap themes), but you get so much more with a real coded style. Bitmap based themes don't follow your color scheme. And they tend to be slower as well.
But if you really want to do a bitmap theme, checkout the Marble theme that ships with KDE. Or the System theme, which uses the same engine, but uses gradients instead of pixmaps.