There's a lot of truth in this.
There's enough exemptions / reliefs that anyone who's employing specialists to manage their affairs should be able to avoid most of the inheritance tax hit if they so choose. Whereas people who manage their own affairs such as a random pensioner who lived frugally and saved their wages for 50 years and ended up with 7 figures in the bank probably won't.
In the case of the Eavii, I think it's fairly safe to say that the reliefs are very much within the "spirit" of the rules for Business Relief and Agricultural Relief - the limited companies are established and actively trading, the farm is working, and both are long standing affairs (presumably) staying in the family so should qualify for 100% relief.