The downside to inheritance taxes is that governments are typically less productive stewards of wealth than family dynasties like the Thomsons.  Thomson Reuters employs 60,000 people in 100 countries around the world, but we'd have to use our imaginations to imagine what the situation would be if the government took a piece when Roy died, then another piece when Ken died.  Maybe risk taking and entrepreneurial gambles would have been squelched?

In Canada, we pay a form of inheritance tax under a different name.  When we die, we are deemed to have sold all our assets at fair market value, and we have to pay tax on any resulting capital gains (principal residence exempted , and some family farms and businesses also exempted up to a limit).  Typically this means something close to 25% of gains during one's lifetime finds its way into the government's treasury.  Presumably, the TRI dividend helps David Thomson to service any debt incurred when Ken died.