I think it is a bit different.  The 30'000 BTC June lot was seized property, and the the government is suposed to auction seized property as soon as possible, irrespective of market conditions.  It took so long only because they had to wait for permission by the court, and "soon" in government means "only a few months". 

This 150'000 lot is still disputed property, and Ross has not been convicted yet, so the government must consider what happens if he is cleared and the bitcoins are determined to be his property (as unlikely as they may think).  In that case, Ross could sue the government for the loss he suffered by not being able to sell them.  That would be bad for the career and prestige of the people responsible.  Thus the agreement.

Auctioning "perishable" goods in these circumstances probably has many precedents.  In any case, after the coins are converted to legal tender, with Ross's agreement, the people responsible cannot be blamed if the price goes up again.  They were as considerate as possible given the circumstances.

Civil servants do not get a cut of the money from the auction; that money goes to the Treasury (or to some general fund for the public good).  They are motivated by gold stars in their resumé, that eventually lead to promotions.  Catching and convicting criminals yields gold stars for all involved.  Carrying out a smooth auction of a weird item, with no complaints of bad press,  also yields gold stars.  They do not care if the auction messes the market or gets a lousy price, but they worry about doing something stupid that could stain their resumés -- such as auctioning a bunch of seized game tickets after the game, or auctioning so much stuff at one time that they cannot get enough bidders for it.