  Kontsevich's characteristic classes are invariants of framed smooth fiber
bundles with homology sphere fibers. It was shown by Watanabe that they can be
used to distinguish smooth $S^4$-bundles that are all trivial as topological
fiber bundles. In this article we show that this ability of Kontsevich's
classes is a manifestation of the following principle: the ``real blow-up''
construction on a smooth manifold essentially depends on its smooth structure
and thus, given a smooth manifold (or smooth fiber bundle) $M$, the topological
invariants of spaces constructed from $M$ by real blow-ups could potentially
differentiate smooth structures on $M$. The main theorem says that Kontsevich's
characteristic classes of a smooth framed bundle $\pi$ are determined by the
topology of the 2-point configuration space bundle of $\pi$ and framing data.
