The US position is that tax on unrealized gains on investments, property, and the like should be imposed on the estate of the deceased, and not on the person(s) inheriting the asset(s). Thus, the inheritors get the stepped-up basis for the asset and pay tax only on the gain (difference between selling price and stepped-up basis) when the asset is disposed of by the inheritor.
Now, the executor of the estate must file an estate tax return to close out the estate when all the assets have been distributed to the beneficiaries and pay the estate tax due, and the executor must plan for this payment (as well as other costs of administering the estate, including settlement of outstanding debts, collection of outstanding loans, the executor's fee, if any). Thus, if the will of the deceased (or probate court in the absence of a will) says "I appoint the law firm of Dewey, Cheathem, and Howe as executors of my estate, and leave all my assets to my sole heir Sonny Boy" than it is not true that Sonny Boy will get all the assets of the deceased as of the date of death: he will get whatever is left after all the fees have been paid and a sum of money set aside for payment of estate tax. Some of the assets might need to be sold to pay for all this, and if so, the estate will pay capital gains tax on that sale, and Sonny Boy will have a stepped-up basis for whatever assets he actually receives as his inheritance after all fees and costs have been paid. Now, it might be claimed that actually Sonny Boy did end up paying for the estate tax (and all other fees) but it is not an out-of-pocket expense for Sonny Boy. As an additional quirk, note that IRA assets are included in the estate for estate tax purposes even though they will become Inherited IRAs for the beneficiaries designated to the IRA custodian and not in accordance of any directions that the will might provide explicitly or implicitly as in "leave all my assets to Sonny Boy". If the IRA custodian has on file an IRA beneficiary designation leaving the IRA to the deceased's niece Flora, then the IRA will pass to Flora and not to Sonny Boy.
All this is fine and dandy but the US also has a combined lifetime gift and estate tax exemption (currently $11.4M) and thus more than 99% of all estates in the US pay no estate tax whatsoever (their value is below the exemption). Thus, in most cases, what Sonny Boy will inherit is all the assets less court costs and whatever Dewey, Cheathem, and Howe will charge as their fee.