You yourself said in a post "To the victor go the spoils".
You included one which was negotiated arising out of a war started by Prussia (fought with Saxony). This is the citation of Arnold D Harvey, 1992, page 63, `After Jena, Prussia, Saxony and the minor German principalities handed over 500 million francs`. There were long negotiations to settle on a sum after the defeat of these states. Napoleon wanted a much higher amount for the actual indemnity, until payment of which he would not withdraw his forces.
In fact the number cited is incorrect, as the amounts were much higher when considering all the categories - cash for indemnities and support as well as "in kind" contributions. See Dumas volume 19, at page 85 of the text as well as the appendix at page 464 (Dumas, Mathieu. Précis des événemens militaires: ou, Essais historiques sur la campagnes de 1799 ŕ 1814, vol 19, 1826).
http://www.google.ch/books?id=hsUg_2gssAgC&printsec=titlepage#PPA85,M1
At best source for the negotiations is Haussgherr, Hans. Erfüllung und Befreiung: Der Kampf um die Durchföhrung des Tilister Friedens 1807/1808. Hamburg: Hanseatische Verlasanstalt, 1935. The Prussian side is covered in Pertz's Stein (Pertz, Georg Heinrich. Das Leben des Ministers Freiherrn vom Stein, volume 2, 1851)
http://books.google.com/books?id=_HAFAAAAIAAJ&pg=PA42#PPA40,M1
Since Prussia decided on war, lost and signed the peace treaty, as well as agreeing to a settlement, it was "legal" under any view of the existing "international law" or "law of nations" or whatever one wishes to call it.
Oh yes, it was a staggering amount, but then again the Prussian defeat in a war they started was staggering. - R