OK.  Then how is that lost revenue made up for?

One of the issues is capital gains.  Let's say your uncle owned a rental house that he bought for $100,000.  At the time of his death it was worth $500,000.  The gain ($400K) he would have realized if he sold it would have been considered a capital gain and taxed at 15%, which comes to $60K.

You inherit the place and sell it the next day for $505K. You only pay tax on the $5K.  The other $400K in gains magically disappeared.  Change the $500K to $500M and it's still the same concept.  

Your uncle wasn't going to miss the $60K - he's dead.  You don't have much cause to complain - you just inherited a net $440K after the tax.  Who gets hurt are the other taxpayers in this country who have to pay the difference.

Apparently it's not true.  Death is certain, but taxes aren't.